Carrots are good to grow with Tomatoes - also with leaf lettuce, chive, onions, leeks, radishes, rosemary, and sage. The onions and herbs are a good repellent to the carrot fly (Psila rosae). Carrots have a dislike for dill, but Carrot roots themselves contain an exudate beneficial to the growth of peas.
Young Radish. . . Nice to grow by your Tomatoes as they repel the two-spotted spider mite.
Here you can see that I planted a long row of carrots and row of radish all of the way down the bed in front of the 17 Tomato plants. Hopefully, the radish with be ready for harvest by July and the carrots a few weeks later.
A bed of french breakfast radish I planted about 20 days ago. Hopefully they will be ready in 10 days or so. If they are beautiful I have agreed to give them to one of americas greatest young chefs Gabriel Rucker of http://www.lepigeon.com/ . . . I believe that he told me that he is using them on his spring duck dish.