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.
Poor little fennnel. sniff