This feeds many people and is extremely easy (but can be customized). I have brought this to several dozen potlucks over the course of the past few years. It's actually sort of embarrassing how easy this is, but like I said, it's yummy and it feeds a crowd.
1 bottle of pasta sauce
1 box of ziti
1 carton of ricotta cheese (the larger size)
Cook and drain the ziti. Put the ziti, the pasta sauce, and the cheese in a large pan and mix them well. Cook at 350 for about 30 minutes. Voila.
parmesan (or other grated) cheese sprinkled on top
add veggies to the store-bought pasta sauce (mushrooms, zucchini, carrots, etc.)
make your own sauce with cans of crushed tomatoes and onions, garlic, and other veggies