well this has been discussed countless times and if you would have searched im pretty sure you would find a couple threads with the same exact title...
but cuz im bored... there are only a few minor details between the two. the video and picture quality of each are going to be identical but the t3i has a few more handy buttons and flip out screen. basically if you are on a tight budget, the t2i will be no different than the t3i, but if you want to pay that extra 200 bucks you get the flip out screen and some more buttons. but i really like the flip out screen on my 60D, just sayin