There are many places on the web for lists of the do's and don't on Companion Planting. Golden Harvest has a good list with information as well. Here is the entry for bell peppers.
- PEPPERS, BELL (Sweet Peppers): Plant peppers near tomatoes, parsley, basil, geraniums, marjoram, lovage, petunia and carrots. Onions make an excellent companion plant for peppers.