I just got a free 2100 points card with Black ops. Normally i only buy points when there is something I actively want on the arcade so I'm itching to spend it. 
 
I'm kind of tempted to get sonic adventure as much as I might end up regretting it and Afterburner climax. 
 
But I'm throwing this out there to you Giantbomb community! What should I get?

Spend it on Zune stuff.

Personally, I'd get Undead Nightmare for Red Dead Redemption, or Joe's Adventure for Mafia II when it releases in 12 days. I personally intend to purchase Joe's Vendetta seeing as I loved Mafia II and I'm eager to extend the game experience further. If you can't decide what content to buy, you could always donate that Microsoft Points card - I know I could make use of it :P

Pass it this way. YOUR KING DEMANDS IT!!!

Super Meat Boy 
Doom II
Duke Nukem 3D
 
apart from Duke Nukem, those are the last games I bought off of XBLA. All worth it.

The Scott Pilgrim game is only 400 points this week, I say it's worth it if you like River Ci--retro beat 'em ups.

 Super Meat Boy  and The Tempura of the Dead

Limbo or Lara Croft are both great and worth the money i think. 

As said already, Super Meat Boy is cool and definitely worth getting. But I'd throw in Trials HD, too. Awesome game with some DLC of it's own, as well as a new pack coming out soon.

The new Pac-Man XBLA game is out this week.  You could wait for that.  If you don't have Super Meat Boy yet, you should get it while it's cheap.