I don't know the Canon line. I stick with name brands (Nikon). However, I agree with musicaleCA - go for glass. I'm still using 20-year old lenses but, during that period, I've replaced my camera body five times.
You have made little sense there...I understand the old glass, Ive used really old nikon glass, and its no different than my brand new nifty 50, only thing different is that they are manual focus, which isnt a problem...almost every other shot with my 50mm lens is manually focuses...the thing is horrible at focusing...
Well anyhoo, you imply that glass in more important then bodys, yet your camera body has been replaced 5 times....hmmmmmmm
To the OP, I would go with the cheaper camera, they are both rather similar, and the cheaper body will let you have more money for better glass, but then again, its not a HUGE difference, im not all to familiar with the canon rebels...but if the specs of the XSi are significantly better, and you feel its worth the extra bit of money, by all means get the XSi.