A thorough comparison of all the cameras would take quite a while, and it would help to know specifically what kind of photography you do. However, here are a few ideas to get you started in your own research.
The Canon t4i / 650D is an excellent camera for a beginner or enthusiast. I've owned both a t1i and a t2i, and I've been happy with the line. Given the proper accessories (lenses, flashes, triggers), it's perfectly capable of doing any kind of photography you want. The line has improved since the t1i and fixed a lot of "problems" (higher resolution, better ISO / noise reduction, faster continuous shooting, supposedly better auto-focusing, better video support), and I can't think of a reason to say, "Don't get a 650D. That's a bad camera."
The Canon 60D, at this point, seems redundant to me. The body costs an extra $50 or $100 compared to a 650D, and you get a mix of upgrades and downgrades. It has the same image sensor, but the 60D has the old DIGIC 4 processor. While it still has ~5 fps continuous shooting, the max ISO is lower. The 650D now uses the same 9 point cross-type AF, so no difference there. What you're getting for your money is a slightly sturdier construction and a different interface (LCD on top of the camera and a wheel on the back). If you hold it in your hands and you like the way it feels, get it. But there's very little on the inside to say that it is a better camera... it's just "different."
Like one of the commenters said, you should keep the Canon 7D in your list. It's an excellent camera, and it's a nice jump up from the 650D. The body is about twice the price (~$1200 or so), but you get some nice upgrades. There are two DIGIC 4 processors, so it can do a better job handling burst mode, delivering 8 FPS (~40% better than the 650D / 60D). It has more auto focus points, for better focusing. It's a heftier, sturdier camera, with a top LCD and a wheel on the back. If you're doing action (i.e. sports), then this is an excellent choice. However, keep in mind that you need a nice f/2.8 telephoto lens as well, and the $600 price difference between the Canon 650D and the 7D will go a long way towards paying for that. A Canon 650D with a nice lens trumps a 7D with a crappy lens, in my opinion.
The Canon 6D is awesome in some ways, but it's not straight up "better" than the 7D. It's got some trade-offs if you do action photography. However, if you're in the studio, doing environmental portraits, or doing something else not action-y, then the 6D is simply an awesome camera. Full frame instead of crop. New CMOS sensor with slightly higher resolution (20MP vs 18MP). New DIGIC 5+ processor. Incredible ISO (25,600). Oddly, it uses SD cards (where-as the 7D and other high end Canon cameras use CF). And despite being more expensive than the 7D ($1800 to $2000 for a body), it has a lower frame rate (4.5 fps) in continuous, fewer auto focus points, and fewer cross-type points. In short, incredible image quality but worse features for action photography.
So there's a quick overview. It's up to you to figure out what you want to do with the camera, and which is best for your needs. For my money, I'll take a 7D, but I'd also be interested to see if they release a newer version in the next year or two that incorporates dual DIGIC 5 processors instead of the dual DIGIC 4.