The Canon Rebel T3i takes the consumer level dSLR a couple steps closer to the mid-level Canon 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.The T3i shares a similar autofocus system to the 60D, with 9 focus points and three auto focusing modes. However the 9 AF points of the 60D are more sensitive than those of the T3i: all are cross-type in the 60D, only the center is cross-type in the T3i. The 60D autofocus system is much less complex than the sophisticated AF system of the 7D with its 19 AF point system and its additional Zone, Spot, and Expansion focus modes. These various modes address how you want to deal with and group the numerous AF points. Plus the custom settings of the 7D allow one to customize how the AF system works - how it tracks subjects, how it deals with objects that come between you and your initial subject, how quickly it responds to these changes of possible subjects that are at different distances from you, etc.
If you are thinking of T3i T2i vs Rebel, Rebel T3i T2i pay. Since both cameras have the same 18 megapixel sensor and DIGIC 4 processor, so T2i T3i and create files in exactly the same image quality, producing the same low light / high ISO sensitivity, shooting at 3.7 fps, and is almost same size and build quality. Both are offered the same 18-55mm lens kit (with a couple of small cosmetic differences between the new kit lens T3i). T3i is slightly larger and heavier because of added rotation back LCD. And it is one of the biggest differences between the two cameras.
As you can probably find the prices at which each camera is not built the same. Construction T3i a relatively strong stainless steel chassis with polycarbonate body. The 60D has a durable aluminum frame and lightweight polycarbonate body, but not as strong as design 7D magnesium alloy. The 60D also has a certain amount of seal time - more T3i, less than 7D. But for most users, including those who use the camera a day, or in situations Travel, building one of these cameras much more than good enough strong enough and durable.