I have a T2i that I use strictly for video. The firmware kenafien is talking about is Magic Lantern - simply amazing. Basically in addition to the manual aperture/shutter/iso settings, it gives spot-metering readout, live histogram, audio gain control, focus peaking, follow focus control via camera, expanded ISO for stills/video and a whole slew of other features you'd only find on high-end video cameras.
Here's a full list of features on their page, with video examples:
http://magiclantern.wikia.com/wiki/550D
On the downside, the rolling shutter isn't exactly ideal for video, so there's still issues with video looking jerky if you're not using any stabilization. Also, the onboard audio isn't great, even with the manual control. Add a decent stabilizer like the Merlin Steadicam and an external mic or recorder (Zoom H4n is a good choice) and you have a very nice platform for making movies. Downside is the price of Canon lenses - luckily adapting my old m42 lenses is as easy as buying an adapter.