Mass Effect, Mass Effect 2, Lost Odyssey, Rez HD, Tales of Vesperia, Psychonauts, Halo Wars, Fable II.

Fable 1,2 and 3 are freaking amazing games. I don't have a 360, but if I could afford it, I would buy it just for Fable.

I recommend that you read more reviews about Dance Central (which I'm sure you did) just to make sure that you won't get disappointed when buying one.
http://www.metacritic.com/game/xbox-360/dance-central/critic-reviews

I'm not sure what kind of RPGs you like, but I'll list the ones I liked/loved or the ones most people liked.

• Mass Effect Mass Effect 2 (TPS/WRPG) - GREAT series that you shouldn't miss. Buy the PC version if you have a really good PC.  (Gameplay video)
• Lost Odyssey (Turn-based JRPG) - A great JRPG made by the legendary Final Fantasy creator Hironobu Sakaguchi. If you're looking for a classic FF. This is the game for you. Keep in mind though that the battle system is very slow (I don't mind that personally), the story is quite bland and has a very long loading times. But it's still great game overall. (Gameplay video)
• Tales of Vesperia (ARPG) - Not a big fan of the Tales of series, but the game got good/great reviews in general. Check it out (Gameplay video)
• Bethesda WRPGs - Oblivion and Fallout 3 - Not sure if you own any them on PC or PS3. Check either of them out. You're bound to like one of them. (Oblivion gameplay video) - (Fallout 3 gameplay video)
• Dead or Alive 4 (Fighter) - Probably the only good fighter (exclusive) on the X360. (Gameplay video)
• Multiplatform Fighters - Super Street Fighter IV - SoulCalibur IV - BlazBlue: Calamity Trigger.
  
• Gears of War Gears of War 2 (TPS) - One of the best TPS games this gen, IMO. (gameplay video)
• Bayonetta (Hack&Slash) - The best hack&slash this gen. If you like Devil May Cry type of gameplay you'll probably like this one. (gameplay video)
• All the great platformers are available on Xbox Live Arcade. 'Splosion Man, Super Meat Boy, LIMBO, Braid. There a lot of excellent titles on XBLA.

If your getting it mainly for Dance Central, then you'll probabily be interested in some of the other fitness/sports games on there. as i dont have one, if i was going to get one it would be for Mass Effect, but then thats a moot point now, so next would be Lost Odyessy, Tales of Vespira, Alan Wake and maybe Gears of War, because its not FPS.

Thanks for the input guys, I have to say that from the comments here it looks like I will absolutely love Lost Odyssey!

For Mass Effect, I do have a great gaming laptop but I like playing sitting on my couch more than on my computer chair so maybe I'll opt for the Xbox 360 version.

I'll have to check some review for the Fable games to see what kind of RPG they are.

@Fab_Gs: If I remember correctly Bayonneta is multiplat but runs much more smoothly on Xbox 360 right?

Also... has anyone actually played Dance Central here?

Anytime! I'd recommend going for the Brutal Legend pack in then. I absolutely loved that game. I'm not really a fan of Jack Black but in the right setting with the right role and the right supporting characters he can be fun. That game is one of those situations. You can also trade in Forza 3 and Brutal Legend and get like $10 trade in towards another game

I don't wanna be a bitch but if all you are going to do is play dance central then you should use that money to take real dancing classes instead with a real instructor who can guide you on the spot, not a video game.

This thread reminds me that why in the hell there are so few turn based JRPGs on HD consoles !? Everything seems to have action based combat system nowadays. This saddens me greatly. =(

I know those were directed at Fab_Gs but I'll butt in anyways because I'm bored at work. Yes, Bayonetta is one of the multiplats that performs more smoothly on the 360. The PS3 version had a patch which fixed things up quite a bit I believe but the 360 version still edges it out in detail. For how quick the game is though I don't think many would notice unless they were right next to each other.

As for Fable... Hmm... it's hard to describe because there really aren't many games like it. And it's really a "love it or hate it" kind of deal. I love it. I don't want to say it's like Assassin's Creed 2 but for some reason I get the same vibe from them. Both have swords and guns. AC is more historic in presentation while Fable is more fairy tale. Their music equally support their atmosphere (AC: Historic era and exploration and mystique, Fable: Adventure, fairy tale cuteness and lightness). And in both games you can see your actions shape the world albeit in different ways. In AC your own village changes based on your investment into it and in Fable soem pretty black and white decisions throughout the game change environments, you can make business investments and such, etc. If you liked those community elements in AC2 you might want to check out Fable 2 and 3 as they do similar things with similar gameplay.

Alan Wake and Lost Odyssey. mostly  anything else it multiplatform that aren't shooters, but ur intrust is not in shooters so just those 2 and a hand full of DLG's, but still you'll find some of those games on PSN.