Peas are a great companion for peppers. Peas and peppers do not compete for nitrogen or other nutrients in the soil.
Basil plants are excellent companions to many night shades. It is said to boost the flavor of your peppers.
Eggplant and peppers are in the same family so they have all of the same needs making them good companions.
Carrots and peppers grow well together. The carrots add some weed control and also help create the humid growing conditions peppers like.