I second (third? fourth?) the recommendation of the Asgard on Wednesday nights. I've never been to Razzy's, but I've heard good things. I went to the Limelight once, and it was awful. The backing vocals on the karaoke tracks were so loud the singers couldn't be heard. And I've heard good things about Courtside, but you have to get there really early, or you won't get a chance to sing. It gets packed fast.