My favorite dive sites in the caribbean are in Dominica.
Dive with Nature Island Dive. Great for advance divers, small groups. Great night dives with lots of inverts. Great color. Lots of large sponges with crinoids as back drop.
Check out my reviews at http://www.scubatripreview.com/index.php/caribbean/dominica.html
Dominica is truly one of the best spots in the caribbean.