Martha's Vineyard
Sue and I went to Martha's Vineyard a few autumns ago with the bikes. There's a state park in the center of the island that has some off road trails. Not real mtn biking (mostly flat and sandy) but I enjoyed and at least one can get some off road mileage there. Plus biking the roads thoughout the island can also be very enjoyable. The eastern side of the island has lots of clearly defined bike paths, sometimes integrated with the road, sometimes a complete separate path. Nice place to visit, great little restaurants, some nitelife, quaint surroundings, great beaches and great views. One can also rent mopeds for the day to tour the western side of the island including the Aquina cliffs.