When I was in school I used to put the "lite" ranch on my baked potatoes... lots of flavor with slightly less calories than your traditional toppings :)

A yellow curry with peas, okra, and cauliflower.

laughing cow cheese! It's very light, and tasty

I sub greek yogurt for sour cream (on baked potatoes but also tacos, perogies, etc.). Fresh dill and/or scallions are also really good. Or sauteed onions (light on the oil). Smoked salt or smoked paprika fills in for that bacon-y flavour, too.

Some cheddar, broccoli, and a little bit of Greek yogurt is always my favorite

How has no one mentioned Sirracha?

I usually just put salsa and slices of jalapeno peppers on mine.

my favourite topping for a sweet potatoe (should work with regular spuds?):

2 strips crumbled bacon
1-2 tablespoons greek yogurt
siracha to taste...so good.

and if you want to omit the bacon- i like adding a runny fried egg + paprika.

that with some arugula is my go-to post yoga meal.

Light sour cream is almost as good as regular, if you're ok with "light" products. I love spice blends, too, especially Penzey's Northwoods Fire.

Hands down, salsa is the best low fat thing to put on a baked potato. Chunky pico de gallo type salsa. I like it with a little fat free sour cream. Delicious!

I also like chili on my potato. I make a low fat turkey chili and will put a little of that on my baked potato and top with low fat cheese and FF sour cream.

I like chili. (Take that however you will, from a can of chili, to a pot of beef simmering all day, to a quick veggie chili. My favorite is a quinoa based vegetarian chili with lots of beans.)

In the same vein (only not), I also like just plain beans. (Black beans, maybe, with some jalepenos and a little bit of greek yoghurt for my wife.)

I second both chili and curry as toppings for a baked potato! Of course, you're pretty much making it the base of your meal rather than a side dish.

plain Greek yogurt
black beans and salsa
chili
sauted greens and a fried or poached egg

Add protein and fiber to make it a meal -- broccoli and cheese, chili, taco fixings or BBQ.

I love the way potatoes taste so much a lot of times I just put salt and pepper on them. A drizzle of Greek yogurt or some lemon juice is good too.

Also potatoes are very healthful, full of vitamin C & iron, so my feeling is use them with anything you would put on pasta or rice (instead of those). My homemade ragu tastes great on potatoes with freshly grated pecorino romano!

I love a sprinkle of truffle salt. It gives baked potatoes a rich and almost buttery taste without the butter.

BBQ! Sliced brisket, sauce, little bit of cheese, diced onion and jalepeno. Basically a BBQ sandwich but sub a potato for bread.

Butter, cheese and bacon are fairly healthy.

Echoing many other commenters: were I one to care about fat content (and I have in the past, but don't currently), I would use Fage Greek yogurt! So delicious, and nearly identical to sour cream.

I recently made Southwestern stuffed sweet potatoes (subbing yogurt for the sour cream) and I think it would work well with regular potatoes too. http://ellysaysopa.com/2012/05/06/meatless-monday-southwestern-stuffed-sweet-potatoes It is basically corn and black beans with a spicy creamy sauce. Delicious!

Hummus! I can't do dairy so I love alternate things like caramelized onions as someone said, salsa, any flavor of hummus, fried egg, or just spices.

tahini, miso paste, hummus, avocado, tomato sauce, coconut milk curry, lemon juice and spices (garam masala, cumin, etc), bbq sauce, carmelized onions, creamed corn. mix and match!

-black beans, guac + salsa
-classic baked beans!
-sautéed garlicky spinach, mushrooms + white beans
-hummus + broccoli

For sweet potatoes I like sweet toppings:
-sliced banana + dollop of plain yog
-drizzle of coconut oil
-almond butter + maple syrup

Peanut butter

We had baked potatoes for dinner tonight! I took pesto chicken sausage out of it's casing, crumbled it in a pan and cooked a whole bunch of thinly sliced swiss chard and minced garlic in the same pan with a little bit of olive oil. Then, I scooped out the insides of the potatoes that I had baked before (leaving the skins), mashed them with a little bit of milk and then mixed in the chard and sausage. I put the mixture back into the skins, topped with a little bit of parmesan cheese and baked in the oven for 20 min at 350- it was filling, delicious, and a great way to eat lots and lots of swiss chard!

Scoop out flesh (like making a twice baked potato) and mix with smoked salmon (I use the packaged 4 oz filets sold adjacent to fish counter). Add a bit of butter/sour cream or greek yogurt and reheat briefly.
Those smoked filets store for about 6 weeks in fridge and are good emergency fodder-- consider using in place of bacon in recipes like chowders.

Blasphemy, I know, but: Bacon salt. (Hey, it's vegetarian!)

My husband and I like to put cottage cheese and diced jalapeno relish on our baked sweet potatoes, with lots of black pepper.

Fat free cottage cheese and sunflower seeds

I like to hollow mine out slightly (like for potato skins, but leave more of the potato) and fill the space with something yummy. I use leftover taco meat with a little cheese, chicken and pesto, but my boyfriend's current favorite is the filling for philly steak sandwiches (thinly sliced beef, onions, and peppers).

It just occurred to me that some pesto would be delicious on a baked potato. Other than that, I like to use up leftovers with them, whatever is bangin' around in the fridge and needs to be used up! Chunks or shreds of meat, sauteed veggies, beans, greens, whatever you got.

Put back potatoes! Bake, scoop out middle, combine with cottage cheese and whatever flavors you want (green onions, cheddar, bacon, broccoli, pureed cauliflower, nutritional yeast) and bake again til cheese is melted.

I like to mix up some chives with those little pink shrimps and sour cream (greek yoghurt works, too), salt, pepper and a bit op lemon juice and heap that mixture on my baked potatos. Works really well with smoked salmon, too.

I like just simple salsa on mine. Lots of flavor, hardly any calories. If it's a meal, add some protein in the form of beans or chicken. Easy, quick and delicious!

We like to put refried beans (actually pretty healthy), fresh salsa, and cheese or sour cream on baked potatoes. It feels like a complete meal, and it's super simple.

I love to put some spicy brown mustard, salt, and pepper on mine. And, to second, third, and fourth others...greek yogurt is amazing on spuds.

Greek yogurt, a sprinkle of caviar, and a few chives.

Italian dressing

If I'm being good I'll have cottage and cheddar cheese on a baked potato, but nothing beats leftover chili with sour cream and cheese if I'm not.