You could grow a few edible flowers to attract bees and add to salads.
Sometimes I grow marigolds in the middle of a bed of tomatoes. They are supposed to be good companions.
French Marigolds are a good companion for tomatoes as they are nematode fighters, Burpee has this one,just to kill nematodes.
http://www.burpee.com/flowers/marigolds/marigold-nema-gone-prod000268.html
I was looking for companion plants for my fennel, and read, “Fennel has no friends.” For some reason, that made me feel sad. So, my fennel is in a smart pot..all ostracized from my other plants.
I have tried marigolds but not enough steady sunlight for them. Bummer as they are so pretty. Also transplanted Swiss Chard into the vegetable planter. Lettuce will do fine there as well.