We did the South Beach diet for just a little while, and we only really did counter service places while we were on phase 2.
Many, many places have salads, just ask for no croutons or bread.
We would also do something like the wrap at Pecos Bill's, with the carrots. It's not whole wheat, but it would help us in a bind.
The Tangierine Cafe at Epcot is also very good for SBD. I believe the bread there is whole wheat, also.
Most restaurants will make substitutions or remove something if you ask, in our experience. My aunt is on the Atkins diet and when we went to the Tusker House, they gave her twice as many green beans, and no potatoes.