Some beneficial companion plants for chili plants include basil, marigolds, and petunias. Basil helps repel pests like aphids and spider mites, while marigolds deter nematodes and other harmful insects. Petunias attract pollinators, such as bees and butterflies, which can aid in the fertilization of chili flowers. Additionally, planting chives or onions nearby can help deter pests like aphids and thrips.