Veggie chili is easy and relatively cheap. You could also do a spaghetti bolognese with tofu instead of ground beef. That one has been a big hit with my meat eating family. There's also always the option of making a big pasta dish with lots of veg, and then grilling meat or your other protein choice on the side, and then letting people add it to their pasta as they wish.

-tacos with tofu filling
-vegetable enchilladas
-vegetable curry
-make-your-own pizzas

Salad with black beans, corn, red onions, edamame, and cilantro; sesame peanut noodles (with optional tofu or chicken); taco (or burrito) bar with vegetarian/vegan and non-vegetarian options; cold soups (gazpacho, melon, strawberry); roasted corn is always a crowd pleaser; wild rice with nuts, fruit, and a nice vinaigrette; stuffed portobello mushrooms (made vegan, vegetarian and non-vegetarian, which can also be substituted for burgers if you're grilling for the rest of the crowd), and for dessert - any fruit pie can easily be made vegan, and sorbets are great for the beach!

Any type of 'make your own' bar works well for large groups of people with different food needs. Choose ingredients that will make everyone happy. Ones we've used:

Potato bar
Salad bar
Quesadilla bar
Pasta bar
Pizza bar
Sandwich bar
Taco bar

You can also do buffets, like Mexican, Chinese, or Indian food. I'd offer up one meat and one vegan entree with vegan sides.

I'd prep food ahead and bring food in containers that it can be re-heated and served in, like pyrex dishes, as much as possible.

Ratatouille!
I agree with fabricwench, bars are a great option for a large group. I'd add a polenta bar to that list. For a vegan taco filling, you can also make refried beans (or get some cans).

On the grilling front, my (extremely carnivorous) family LOVES the Field Roast brand of vegan sausages - they started buying them for me when I went vegetarian and have continued even though I live on the other side of the country now. The Smoked Apple Sage one in particular is delicious (we serve it with caramelized onions and sauerkraut on top). http://www.fieldroast.com/products/food-service/field-roast-sausages/

Also, nothing beats a juicy gilled portobello as an alternative burger or make-your-own (veggie or meat) kebabs on the grill. Oh, and one heads up for combined meat/vegan grilling - be sure to keep the vegan area of the grill free of meat juice/residue (that goes for the grilling utensils as well). :)

Just make sure that you don't alienate the other 14 in catering to the 3 vegans. You know your guests better than we do but if I my family was invited to a party and the host served lentil stew or tofu tacos we'd be hitting up fast food on the way home.

If pots/pans are limited, you might consider bringing along a slow cooker, if you have one. Here is a great site that I found recently with easy recipes that don't rely on canned soups: http://www.slowcookerfromscratch.com/search/label/Vegan

I'll echo MK710's suggestion of ratatouille, especially if you will have access to great vegetables.
Perhaps you could offer the meat eaters a sausage on the side. Like Braisenwoman, I am a fan of the field roast sausages, but if you can't get them, I think the vegans will be satisfied with a fresh seasonal stew and some great bread.

Beer chili! A dark, smoky beer can give a totally vegan chili a bacon-like flavor--and of course, all the alcohol cooks out for the kids. Bonus: plenty of leftovers for lunch and snacks later, like nachos or chili fries.

Tacos all the way. Don't bother with tofu or fake meats, just some well seasoned black beans that the vegans and meat eaters will both enjoy. Lettuce, tomato, avocado, jalapenos, salsas, black olives, black beans, (vegan) refried beans, corn and flour tortillas. Non vegans can also enjoy sour cream, cheese, and seasoned ground beef or turkey. Easy to throw together with the simplest of kitchen setups and always a hit.

If you're looking to keep things cheap and minimize dishes (yes, a taco bar with tons of fresh vegetables, salsas, etc, would be amazing, but...a lot to provide for 17 people!), pasta or chili is the way to go. Tomato sauce, cheese-free pesto, and spicy peanut sauce go with lots of vegetable add-ins and are pretty broadly appealing, and a good bean chili is pretty satisfying.

Recently made a great batch of Asian-style rice noodles with peanut sauce and vegetables- would be great with tofu/grilled meat as well. Holds at room temperature nicely.

Also I once made some vegetable and cheese turnovers/hand pies with Follow Your Heart vegan cheese- very good!

@Battra and the others who say that serving perfectly good food isnt good enough for you, stop acting like 7 year olds.

@Jenawithonen: Amen!

That right there is a challenge!

I'll echo: Chili is a super easy and cheap way to satisfy meat and no meat eaters. Do three different beans, dark beer as suggested, and have crackers(make sure they are vegan) rice or quinoa, sour cream, and cheese on the side.

Taco bar is also a great option.

Avoid stir fries as they are hard to cook for 17 people.

Limit salad bars, as no one will be satisfied from them, but they are an option.

Curries (as the editor suggested) are not great. Usually too adventurous for a group.

For grilling: do skewers of peppers, mushrooms, onion, and pineapple based in BBQ sauce. It is amazing and easy to modify for omnivores.

Rice pilaf with almonds, raisins, spinach, tomatoes is a great dish to have fun with.

Tempeh burgers are easier and more filling than tofu. Grills easily and great texture.

Hope this helps.

I make a mean vegan fajita:(This recipe serves 6 and non-vegans can jazz it up as they like)-- the best part? You can pre-chop almost all the ingredients and just throw it all together on-site.

1 large onion (sliced)
2 cloves garlic (minced)
1 Thai red chilli (chopped)

1 each red, yellow and orange bell peppers (sliced)
1 can each kidney and turtle [black] beans (drained and rinsed)

1 tsp cumin seeds (whole)
1 tsp ground coriander
1 tsp greek oregano
1 tsp ground turmuric
1 tsp tarragon
salt and pepper

1 large handful cilantro leaves (chopped)

1. Fry onion, garlic and chilli together on high until onion is transparent. Add bell peppers and continue to sauté until peppers begin to soften (about 5 mins).

2. Add beans and dry spices, toss to coat and allow the beans to heat up (approx 2 minute). Cover and simmer 10 minutes. Adjust spices to taste and toss in chopped cilantro and toss. Serve.

Serve it with a plethora of fun stuff for people to decorate their fajitas with.... guacamole, chopped tomatoes, hot sauce, salsa (red and verde), sour cream, sharp cheddar, cojita, lime wedges, more fresh cilantro. This way you'll please the vegans and non-vegans alike.

@Mirabella & @Battra: I don't suppose it's occured to either of you that some people are veghan out of medical necessity (I know at least two people). Truly, would it actually *kill* you to try something outside of your very limited bubble? You might actually be surprised. Veggies are amazing if you know how to prepare them with spices and different cooking methods. I've made several vegan recipes for avowed carnivores and they've been totally floored at the fact that I've made something so delicious without any kind of animal product involved. [FYI: I'm not a vegan. Not even vegetarian... I just limit the amount of meat and animal products I eat for personal health reasons]. As @jenawithonen pointed out... grow up.

Ooh, I've gota a million suggestions! But I'll try to keep it brief.

You can make homemade grillable vegan beet burgers. You could make them ahead.

And I've got creamy vegan coleslaw to go with (Almond aioli is the dressing!)

Or a creamy delicious pasta sauce with zucchini, white beans, basil and walnuts. Pasta is always easy to make! And the sauce goes together really easily.

Or a summery stew with black beans, hominy, zucchini and corn. I served mine with millet, which was delicious, but rice would work just as well. Or couscous or quinoa.

Vegetarian chili with cauliflower and two beans. Smoky and spicy.

I made some tacos with yellow squash, chickpeas, corn, black beans and a pumpkinseed basil sauce, but I haven't written up the recipe yet!

I just got back from a family vacation!

We made this: http://www.thekitchn.com/recipe-braised-coconut-spinach-chickpeas-with-lemon-164551 (easily scaled up for lots of people and each person got their own sweet potato! Everyone loved it!)

We also made a few things from this cookbook that I absolutely love: http://amzn.com/1592333745 (spicy bean burgers were a hit too, with a side of baked sweet potato fries or kale chips)

This chili recipe also scales really well: http://allrecipes.com/recipe/the-best-vegetarian-chili-in-the-world/ (we don't ever put in the veggie burger crumbles and its still really good)

@ Mirabella, I think jenawithonen was responding to her perception of the unspoken if-it's-vegetarian-it-can't-possibly-be-tasty slant on a couple of comments. Though she might have said it a bit nicer. :) Also, while you might not appreciate a separate area of the grill for your non-meaty items, many vegetarians/vegans truly do. Grilling is messy, and it's nice to know your zucchini hasn't been soaking up hamburger juice. No one is trying to make anyone's life difficult. But the poster asked for suggestions on how to make everyone comfortable, and that was one of mine, speaking from experience.

Thanks for all the great suggestions! I eat meat but I eat vegetarian meals all the time (not vegan though). However, there are some diehard carnivores in the crowd so I'm going to have to provide some kind of meat option. A taco bar or pasta are great ideas and lend themselves to having meat available for those who want it.

@jenawithonen, yes! There is so much hostility towards vegetarian food on this board that it's hard to believe that these people posting are adults capable of functioning in society.

I highly recommend this vegan site, which is family-focused. I am not a vegan or a vegetarian, but it's full of delicious eats that please a lot of palates! The name says it all...One Happy Table!
http://onehappytable.wordpress.com/

I make a great creamy carrot soup with coconut milk instead of cream. If you invest in a stick blender you can make really smooth fantastic soups out of pretty much any vegetable you please. We have made great soups from parsnips, acorn squash, and white beans all made with vegetable broth, olive oil and coconut milk for our vegetarian and vegan friends. With some crusty bread and a big salad on the side, it's much less expensive than purchasing fake meat or processed vegan foods.

Pasta is usually a safe bet and almost everyone likes it. Make a fresh sauce and make sure your pasta of choice doesn't contain eggs. A nice salad, good crusty bread, wine, a variety of sorbet flavors for dessert and you're done. And nobody will be running for fast food afterwards.

Tacos are also a really good suggestion; I know people hate on fake meat a lot, but I reguarly make tacos using Morningstar Farms' fake beef crumbles and a packet of Old El Paso and my teenage SIL (who routinely complains if she has to eat something vegetarian) actually prefers it to real meat. Most people can't tell the difference between that and something from Taco Bell once you season it. Something to consider if you are looking for a crowd pleaser that everyone can share. (Of course, if your vegans are of the variety that believe even pretend meat is evil, stick with pasta.)

There is childishness all around here: we Americans find ourselves in the social position of entitlement: we expect people to cater to our own tastes and our own needs. Meat eaters are sometimes ridiculously fearful of trying a veg heavy dish with kale, tofu or who knows what else. People with dietary restrictions often take offense at a lack of options designed for them. If you don't eat what is offered, why on earth should I feel bad about myself? If I offer you food, you should have the social grace of being grateful for the offer whether or not it pleases you. And there are some dietary choices we're expected to tolerate and accommodate, and some are open season. I grew up Mormon, and no one ever held back telling me how difficult it was to offer me a beverage since I didn't drink tea, coffee, alcohol, or soda with caffeine. When I was traveling through Germany, I was mocked because fruit juice and milk were only for children. But I never failed to recognize that not only were people offering me something, they were going out of their way to offer something that would be pleasing to me. I actually try to please the palates of my guests even though I find vegans tiresome. I have a great recipe for Khatte chhole--a curried chick pea recipe, that has proven to be very popular amongst vegans, gluten free, and omnivores. I think there are two or three secrets: avoid bad meat substitutes because they are divisive. Choose something with robust flavor. If something has a lot of vegetables that is grand but have another dish that uses other kinds of foods for those who are afraid of leafy greens, bitter flavors, or the like. And if a guest has impossible restrictions, invite them to the party and say: my menu is a, b and c. Can you bring an appropriate dish for the party because I would love to share your company, but I am overwhelmed by your dietary needs. Or ask for a recipe, if you want to go out of your way for the guest.

our vegan family just went beach camping with our non-vegan inlaws. hands-down, everyone's favorite meal of the week was when we all built our own foil dinners. the omnivores in the crowd put homemade burger patties in theirs with all the veggies. our family just used potatoes, onions, zucchini, carrots, and mushrooms with a drizzle of olive oil (necessary if there won't be any meat juices) and some yummy seasonings (nutritional yeast, oregano, salt, pepper...). my husband added some field roast sausage that has been mentioned in earlier comments. you can find those at sprout's or whole foods and they cost around $5 for a pack of 4. our relatives wouldn't believe the apple sage sausage was meat-free until we showed them the label :) ten minutes on each side on the hot coals and they were done! the non vegans added cheese to the top of theirs and we all added ketchup. the veggies were all chopped in the morning before we headed down to the shore from the campsite, so all everyone had to do was assemble, cook, label with a sharpie & dig in! it was especially great for the kids in the group, including my toddler who gobbled up all the smoky, seasoned veggies. good luck and have a good time!

I posted this question before we went on vacation earlier this month. Here are the dinners that were made during the week (one by my family, the rest by other families staying with us):

taco bar with guacamole, cowboy caviar, lettuce, tomatoes, cheese, sour cream, salsa, taco meat, soy crumbles, tortillas, and tortilla chips (my family made this based on suggestions here and it went over well)

pasta with veggies and sauce with meat on the side, salad

homemade pizza - 2 meat, 2 veggie, and 2 vegan (with a special crust but I can't remember what they said they made it with)

chicken parm (with vegan chicken patties and no cheese for the vegans), salad, bread

burgers, grilled portabella mushrooms, baked beans, roasted potatoes (the vegans cooked some vegan sausages to round out their meal)

Thanks for all the great suggestions!