[Elizabeth]

Any color carrot will work, they all bolt sooner or later. They readily re-seed themselves. If you let them go to seed you will have lots of carrot "weeds" for the next couple of years. Not necessarily a bad thing, but they will come up sometimes several feet away from the mother plant.

Cosmos also readily re-seeds. Plant them once, and you will have them forever (not a bad thing, I think they are pretty). Once the seeds have matured little birds will be attracted to the garden - they love cosmos seeds and will perch on the flower and munch away, even if the plant bows a bit from their weight (it bounces back). Some varieties will grow quite tall (several feet) so you may have to yank volunteers that threaten to overshade crops.

I second the keeping Lemon Balm in pots (ditto with spearmint). It spreads by seeds and by underground stolens.

Yarrow forms clumps with deep roots and is hard to dig up once established, it seems to become one with the soil, which is probably why it's fairly drought tolerant.

Tansy can become invasive. Both tansy and yarrow are kinda stinky, sort of like the smellier kind of marigolds.

Sweet alyssum readily re-seeds (oh man, does it re-seed LOL)

Queen Anne's Lace can get really big (tall and wide). Since it is such a close relative to carrots I would stick to carrots as a companion in the garden, the same beneficials will be attracted to both. When the plants are small they look too much alike and you might harvest QAL thinking it's a domesticated carrot.

Closely related plants are probably going to entice the same beneficials to your garden so you can get away with just one or two in a family. All of the Umbelliferae (Angelica, Yarrow, Carrots, Cilantro, Parsley, Fennel, Lovage, Celery, Caraway, Dill, Parsnips) will attract ladybugs, parasitic wasps and predatory flies for example.

Basil will mostly attract butterflies, it's not really used to bring in predators.

Diversity in your plantings, interplanting and allowing some plants to flower and go to seed will improve the general health of your garden. Nature on it's own keeps things in balance in the insect wars. It's only when we plant jillions of a particular crop in close proximity with no variation that the bad guys get out of hand.

If you want to get into companion planting, I second Babice's recommendation, "Carrots love Tomatoes", it is a good starting point. Another good book is "Good Bug, Bad Bug" by Jessica Walliser. The good bug section lists plants that attract each beneficial insect.