Bell peppers can be used in a lot of things--you can stuff them with cooked rice or other grains, a bit of cheese, and bake them, you can use them as a filling for an omelet or just throw them in some scrambled eggs, or you can throw them into a pasta salad or a rice pilaf if you like. Bell peppers are also one of the three ingredients in the "holy trinity" of Cajun cooking (along with celery and onions), which is a base for a variety of dishes.
http://en.wikipedia.org/wiki/Holy_trinity_(cuisine)
I often just like to eat them raw. They're juicy.