The Canon Rebel T3i takes the consumer level dSLR a couple steps closer to the mid-level 60D with the addition of the rotating rear LCD screen, remote flash firing, and in-camera processing features.
The already highly competent, older Rebel T2i already shared many important features with the 60D (and even features of the semi-pro 7D) including the 18 MP sensor, 63-zone exposure metering system, high ISO performance, HD movie capabilities, and Digic 4 image processor. With these new upgrades, it might make it even more difficult to choose between them. But there are some important differences.
You can download the user manual for the T3i here.