I started with the T3i, and while an excellent camera I am pleased that I shifted to the 7d.
I like to shoot sports, and the 7d can take many more pictures per second (nearly 8 per second, 3.7 for the T3i). Also it has 19 AF focus points, compared to the 9 on the T3i.
That being said, the T3i can produce some excellent images. Better glass really helps in that area. Any lens you can put on the T3i the 7d can use. So if for budget concerns the T3i is in the cards now, invest in great glass and upgrade the camera later.