There is a nice bike path that along 79 up to the intercoastal. And there's a path the bisects that running parallel to back beach road. I've never been on it and I'm not sure how far it goes. It was planned to run pretty much the length of PCB but I don't know if it was ever completed.
30A used to be nice to ride, but it's usually too crowded now.
If you're looking for long rides there are miles of relatively empty country roads on the other side of the intercoastal.