Really any soup can be made in the good ol crock.

Italian wedding soup

Chicken and wild rice

Tortilla soup (can easily just leave the beans out)

There is one floating around Pintrest that looks good. Lasagna Soup (http://www.afarmgirlsdabbles.com/2011/03/24/lasagna-soup/)

http://www.kalynskitchen.com/2012/11/recipe-for-spicy-slow-cooker-soup-with.html

My crockpot cookbook came with a recipe for potato and mushroom chowder that I quite like. It is a bit creamy (has 1 cup of milk I think), but definitely not a cream of such-and-such type soup. I just went to look for the recipe so I could list the ingredients for you, but I couldn't find it! I'm sure it wouldn't be hard to find a similar recipe, though, or just make it up. I think it would work well for a soup party because there are infinite options for toppings that people could select from--green onions, bacon, fancy croutons, shredded cheese, etc etc.

Side note: I will say that, in my experience, crockpot soups are much better if you saute the aromatics and any dried herbs in olive oil or butter before dumping them in the crockpot. That's one of the tips in the "7 tips" article linked above, and it is well worth the time.

Good luck! Sounds fun.

Jamie Oliver's sweet potato and chorizo soup. https://foodfolio.net/recipes/35608/jamie-oliver-sweet-potato-chorizo-soup/

While it's a thick soup, there's no cream in it, and I think it could be cooked in a slow-cooker just as easily as on the stovetop, and then blitzed with a handheld mixer. Best soup ever.

Pork, Pineapple, and Acorn Squash Stew in Slow Cooker

Olla Gitana
Dairy free, but has green beans and chickpeas; must be adapted for slow cooker. You can swap the green beans for another green veggie. Could swap a ground nut or such for the chickpeas if they annoy you. I didn't notice them when we did this on the stove. The tomatoes vanish completely.Everything melds nicely. Could use veg stock, chicken broth.

The curried vegetable and chickpea stew listed above is amazing. Make it!

The only thing left that I can think of is an italian sausage soup. There's a really good one on allrecipes. I dont remember what it was called. Probably italian sausage soup.

I love that curried vegetable stew that's linked to above. It's one of my favorites - so so good!

Beef stew comes out great in the crockpot!

zuppa toscana-that might be the italian sausage soup mentioned above- spicy sausage, potato and kale- it does have a little cream that you add at the end.... but you could leave out if someone doesn't do dairy or pull their's aside before you add the cream....i love that little bit of cream at the end - I recently brought to a potluck for work (in the crockpot) and everyone loved the recipe!

Whats wrong with a plain chunky tomato soup? Tomato, veggie stock, a little touch of onion and basil.

You can mix and match all sorts of ingredients, and still ensure you have a great-tasting soup! http://www.littlekitchenbigflavors.com/one-recipe-fits-all-crockpot-soup

I like something with chuck roast b/c you and cook it in the soup and pull it out to shred at the end. I generally just add a bunch of good veggies, canned tomatoes, beef broth, seasonings and seasonings. I have made beef stew many times in the crock pot too.