I have a XSi. Although it is a fine camera, I wouldnt buy it new. 550 is too much for it. See if you can find a body only used on CL. I bought mine (body only + 1 8 gig SD extreme III card + 2 batteries) for $400 from CL almost 1.5 yrs ago. So Im sure you can find it for cheaper now. CL can be hit or miss, but as long as you test out the camera thoroughly along with all the camera functions and check the sensor (put the lens cap on, cover the viewfinder, and take a 30 sec exposure. Then check the image for any hot spots), you'll be fine.
And instead of the kit lens, get yourself a Tamron 17-50 lens.
But I will say that I played with my friend's T2i, and that camera is much much better in low light than my XSi. But that camera will be a lot more.