Nutritional yeast is tasty, but make sure you get actual "nutritional yeast" (a yellow yeast, specifically grown on molasses) and not "brewer's yeast (a waste product of the brewing industry, that is more tan, and is often bitter).
I used to eat a lot of NY on popcorn, as others have said (spray popcurn with tamari/soy sauce---a glass plant mister works well for this--then sprinkle NY on top). Years ago, a lot of veggies used to take it with OJ (about a tablespoon of NY stirred into a tall glass of OJ...sounds odd, but actually tastes very good).
Just be aware that NY can be hard for some people (and animals) to digest, and it causes REALLY bad smelly farts sometimes, especially if you use too much at once. I once met a cat who ate a lot of NY, and while he was sitting on my lap, getting some pets, he let out the most aweful 'silent but deadly' fart: I could barely stand it! A friend of mine has the same problem when she east NY 'gravy' (maybe because she doesn't eat it often?).
Red Star Nutritional yeast (also called "Good tasting nutritional yeast") always has B-12 added to it.
"The Ultimate Uncheese Cookbook" has a lot of non-dairy 'cheese' recipes in, many of them using NY. I have the book, but haven't tried the recipes, though I've heard they are good: much better than any non-dairy cheese you can buy.