If you are venturing south past the international zone to Bacalar and Chetumal do avoid "Over Blue" a restaurant and bicycleboat rental place on the Costera road. They are very anti-foreigners with Gringos topping the list. Two doors away at 169 Costera is another little restaurant called, I think; Casa de la Laguna which is much better. Boats can be rented at the Club Vela or the Hotelito Amigos. You might also enjoy my personal blog on the life of an expatriate in Bacalar at:
http://www.homepage.mac.com/donfrancisco864/Menu6.html. No night life, no action. Beautiful views, good swimming.