Hmmm... From what I can remember, there's a bit by the library, a bit across the road from Tides (assuming the skatepark next to Tides won't be your bag), a bit round the market square, a bit at the end of the pier and by the timeball tower and a bit by the King's Head/Port Arms, but to be honest, there aren't loads of spots. If you head up the road to Kingsdown, the sea defence rocks there are pretty fun. Dover, Folkestone and Herne Bayaren't far and there's a fair bit to ride in those places. I think they're building new sea defences in Deal too, but no idea what they're like for riding.
What have you been doing there, out of interest?