My brother is visiting, and I realized I have no 2-player games for the Xbox. What would you recommend that has a quick learning curve (he's only here for 2 days)?

I really enjoyed the Gears of War series- its pretty user friendly and full of awesome

GoW is good, any of the Lego games; Batman, Indiana Jones etc. Not sure if Borderlands has a co-op mode on the same console but might check it out.

gears is a fun one, i really enjoy borderlands, you can play coop split screen