I've got the same problem, had it last year also. Moved the tomatoes to the other side of the garden with out luck. As best I can determine it's a fungus that can't be cured. Your supposed to till everything under, cover the garden with black plastic and let the August heat fry the fungus.

Check out "early blight" and see if it looks like what your plants have. It's a fungus that takes hold when the plants set fruit. You can spray with Daconil and that helps control it. This year I'm growing vertically and as of yet, have not had any fungus problems. But in the past, Daconil helped.