Atlantic Dance Hall can be dead. I'm actually shocked it's still operating. Jellyrolls seems to be the party place if you can get past the $10 cover and the dueling pianos thing. I've never been inside there so I can't say if there's actually dancing, but I'm sure you can groove at the bar or something.
Raglan Road at DS gets pretty lively, and although they don't have a dance floor I've seen plenty of people get up and dance.
DS also has House of Blues which turns into a pseudo-club at night and after any shows. This is probably your best bet for a dedicated dance experience.