While the 50D is a nice body, I'd probably recommend that you go with a smaller body just to start with and invest the other money in quality glass. The quality of your pictures will scale much better with good lenses than with a good body.
None of the DSLR bodies will really take a better picture than any other (mostly just a larger photo), but the better quality of glass that you have in the lens (i.e. more pricey lenses) the better quality the image will be when it hits the sensor. Even the new Canon 7D with a basic lens on it will take a poorer photo than a Rebel XS with an L series lens on it.
Also, with the T1, you should note that it records video in 1080p and, depending on your card, you might want to go with something faster. If you got one of those red-boxed generic Sandisk SD cards, it's likely going to be a detriment to your camera as it's too slow to fit full HD recording on it. And depending if you shoot in RAW or not, a slower card in burst mode won't keep up with the camera.
Edit: And also, the guy at Futureshop was right about the difference in the T1i and the XSi. There's three primary differences: the T1i has 1080p video recording (vs. none in XSi), a 15MP sensor (vs. a 12.1MP), and a 3" LCD screen with 920K dots of resolution (vs. 3" w/ 230K). Truthfully, between those two cameras it's going to come down to whether or not you want video. 12MP vs. 15MP is negligible unless you're planning on printing off big posters on a regular basis.
http://www.dpreview.com/reviews/comp...s500d&show=all
Furthermore, you could probably argue that the XSi is actually capable of taking better pictures than the T1, for the sole fact that it's cramming less mega pixels on the same size of sensor. This means better low light performance and more detail as, essentially, you're getting more photo to each pixel resulting in a clearer picture: "From a theoretical point of view pixel density should affect the amount of random digital noise present in an image and the dynamic range in the image the camera produces. Dynamic range is how much detail can be held in shadow areas before highlights begin to loose texture or, how many F stops of light range the camera sensor can capture. Again, in theory, larger photosites (less pixel density) on the sensor should produce less random noise and more dynamic range for any given sensor size." (
http://www.sphoto.com/techinfo/dslrs...slrsensors.htm).