Personally I'd pick a Sony A580 instead of the A55
. You may wonder why ? Well...
First, there's battery life. The Sony A4XX/A5XX series have excellent battery life compared to the Canon Rebel T2i/550D; in fact twice the battery life: 1050 shots compared to 440 shots (CIPA rating). The battery indicator is far more accurate as well: it uses % rather than the four level battery display on the Canon. It also has some handy things like hand-held twilight mode/iAuto, etc. DoF preview, mirror lock-up, bracketing,...it has a lot of features considering the fact it's a step-up camera from what Sony UK's Paul Genge called 'amateur class' - it' still a mid-level camera, not an A700-ish one (sadly ?). Too bad it doesn't have two control wheels, Quick Navi and a pentaprism viewfinder...
Second, the optical viewfinder of the A580 is as large as the Canon, I think. Without compromising live view - which is the case with the Canon. The EVF of the A55 isn't bad, but most people - myself included - would prefer a conventional optical viewfinder.
Next, performance. The A580 has less megapixels (and probably consequently, RAW files which are a bit smaller) but the buffer is far bigger compared to the Canon. 22 RAW images - more than four seconds of continuous shooting at the 5 frames per second top speed (with updated AF and AE (auto-exposure). So it's not only faster, but it will remain faster for a longer time when shooting anything that may require this speed.
On the A580 and its siblings you could also mount a vertical grip in case you'd like to do portraiture, or want to improve the balance between the camera and the lens (when using heavier lenses). You can't do this with the A55, which is a smaller camera.
As far as price is concerned: it depends from country to country. In the UK the 550/Rebel T2i is only a little cheaper (at Warehouse Express for instance).
SSM/NEX-5/18-55 OSS/Lowepro Pro Trekker 600 AW/CompuTrekker AW/Nova 140 AW/Street & Field gear/Toploader Pro 75 AW. And a huge wishlist...My photos on Flickr...