Hi, and welcome to POTN.
All 3 bodies offer similar stills quality shots.
With a heavier emphasis on video, the 60D and T4i are better choices, due to the articulating LCD.
Out of those 2, the T4i is designed even more with video in mind, with the ability to AF on certain(STM-series) lenses..and very quietly so.
A big consideration is the layout and controls; the T4i being a Rebel series, and the 7D having the same controls and layout as your current 40D. The 60D is sort of a cross between the two, with some D series similarities and some Rebel.
If you plan on shooting any sports/action/birding stills, the 7D is clearly the best option...with it's much faster FPS and serious AF abilities. It also has the rugged build(and weight), and some weather-sealing.
The last consideration is price. The T4i is a little cheaper than the 60D, which in turn, is about $400-$500 less than the 7D.
Oh, the 7D uses CF cards, the same as your 40D, so if you have some decent cards now, that would save you from having to switch to SDHC.