Take a look at the Canon EX 270, it works very well with a T2i. Small lite weight, only 2 AA's can last 300-400 shots. It uses the flash inteface in the camera. Amazon has em for $144.
Only problem with that is, that you have zero directional control - part of the idea of putting a flash on an SLR is, that you can bounce it.
-> I personally do not consider a glorified po-pup flash worth any expense.
(Only benefit it has: More power, maybe a bit higher off the camera than the pop-up flash)