Just Dance 3 is set to repeat the franchise's success on not just the Wii, but also on the PS3 and Xbox 360 this time around. You'll need PlayStation Move and Kinect for it, respectively.
The game contains 40+ tracks, some of which Samit has already listed because he is on top of everything Just Dance-related. The Kinect version will offer Xbox Live leaderboards for score-whoring, a "slight difference in terms of difficulty thanks to the full body capture tracking," which will come into play for scoring points with your entire body, and a special Shout Out! feature that lets you and your party crowd score more points when singing along.
The PlayStation Move version also lets you sing along with on-screen lyrics, but otherwise doesn't seem to offer that much extra. The Wii version now offers four-player sequential multiplayer, where players take turns to act out a part of the dance routine for a single song. All versions will have a new dynamic environment that changes as you progress through a song.
I don't think anyone is going to buy any peripheral just for this game, but the Kinect version might give Dance Central plenty of competition when it launches this October -- at least, here in Europe, where practically nobody knows who Harmonix are, and where Just Dance tops the charts for months on end.