In St Thomas the best party deal we've found is the Kon Tiki party raft.
For about $34.00 each you can ride a 'raft' through the bay, check out the glass bottom parts for sunken stuff and fish, and go to a secluded beach for swimming, all the time sucking down unlimited 151 proof Rum punch and listening to a live 4 or 5 piece steel drum band. The ride back is terrific too - they get a limbo contest going and all kinds of dancing.