I was in a similar situation myself a little while back and ended up going with the 50D. some of the reasons for MY decision (which may or may not apply to your situation)
1. I have big hands and none of the rebels felt comfy in them
2. What I call the "VGA screen of Chimpy goodness" - probably won't help you take better pictures, but man is it pretty.
3. The top LCD panel - Being a beginner I am always playing with the settings, it makes it so easy to check what you have things set to and you don't have to leave the main (battery hog) LCD screen on all the time. I use it all the time.
4.The "Gapless microlenses" apparently help improve low light ability over the T1i.
5. after researching the video advantage of the T1i, I was kinda turned off by the lack of autofocus, so I picked up a clearance hard drive camcorder that is 1/3 the size of my DSLR and fits nicely into my camera bag in case I really want a video. Haven't used it yet ouside of when I first brought it home.
6. I wanted something to grow into, that would last me a long time (I'm kinda rough on things), and didn't want to re-learn how to use my camera if I upgraded, the 50D seems to have a more similar layout/controls as the higher end Canons, and seems to be built a little more solidly than the rebel series.
and finally (might get attacked for this one) I went to disney for a weekend right before buying my camera, it seems like the entry level DSLR's (Canon rebels and Nikon d40/d3000) have become the next family P/S camera... everyone seems to have one nowadays. That dosen't make them lesser cameras, I probably just have an ego problem or somehing like that.