Pix, that's VERY cool of you to buy your friend a new body -- even if it is refurb'd. I bought one of my buddies a 60D a few years back and he was really touched by it.
Anyway, the order of bodies in Canon (from low to high) is:
T3 -> T2i -> T3i -> T4i -> 60D -> 7D -> 6D -> 5D III -> 1D X
I left out the discontinued bodies... T1i, 50D, 5D & 5D II, etc. A 5D II would be amazing (even used) but still be more expensive than any "new" Rebel body. Probably more than you want to spend.
The XS and XT were low end (at that time) and the XSi and XTi were the high end. The XT is below the XS. An XT was an 8MP DIGIC II, the XS was a 10MP DIGIC III processor camera. The XTi was the "high end" at that time (pre-dating the T series) at 10MP and then the XSi replaced that ... being 12 MP. The XT series were DIGIC II, the XS series were DIGIC III.
The Rebel bodies (everything that started with an X or T) are also sold as xxxxD or xxxD bodies outside North America. The 2 digit bodies (xxD) are the pro-sumer bodies. They start to have features only found on pro level bodies (weather sealing, a rear dial so you can control both shutter and aperture directly and simultaneously without pressing button combinations to make this happen and more direct-access functions without having to use menus.) A used 60D body would be better than any Rebel body (it's an 18MP sensor but the body is weather sealed, it has a rear dial, more direct features, a top LCD, and all 9 AF points are "cross type"). But I don't know what you had in mind to spend.
The T3 is very basic, but gets the job done. It was released in the same year as the T3i (hence the name "T3" - which means it's newer than a T2i, but it was designed to handle a lower price point and be more economical than a T2i. Even though the T2i is an older body, it's actually a better body.)
There was a T1i (15 MP).
The T2i, T3i, T4i, 60D, and 7D all have an 18 MP sensor. The difference is the processing and other features of the body. All of those bodies have a Canon DIGIC IV processor *except* for the T4i which now has a DIGIC V processor (much faster and does a better job dealing with noise, etc.)
A T3i, T4i, and 60D all have an articulated LCD screen (swings out and twists - like a camcorder). The T2i's LCD is fixed to the back - not hinged. BUT... the T2i also has a proximity sensor on the back and can tell when you put the camera to your face. The display auto-blanks when you put the camera to your eye. On a T3i, T4i, or 60D the display remains lit.
A T3i and 60D have a built-in commander which can remotely fire a Canon flash capable of running in slave mode (such as the Speedlite 430EX II). You do have to engage the pop-up flash to fire the external flash (that's the catch.) The T4i has a built-in radio commander which can fire a radio flash (such as the new Speedlite 600EX RT)... but that flash costs nearly as much or more than many Rebel bodies.)
Mostly what your friend will get from the body (in addition to a bit higher res) is higher possible ISO settings and better (lower) noise handling as compared to your friend's current body.