South Beach has a massive club scene. Being somewhat past it I do not feel competent to comment on where is best to go but I am reliably informed that getting into the popular clubs is really difficult. Should you be looking for the coolest nightspot in town, one of your best sources of information is your hotel concierge. Do not forget to tip him or her.

South Beach Magazine also runs regular articles on where to see and be seen http://www.southbeach-usa.com/nightclubs.htm