Power mentioned not to worry about pixel parameters, and he's 100% right, anything beyond 8mp and unless your in this for professional quality stuff your eye will never see the difference.
The XSI and previous model XTI are great cameras. I was using an XTI heavily when I first came to these forums and people were really took notice of my shots while I was in that body. I've seen plenty of low shutter count XTI's out there. Check Fredmiranda, adorama's used section and even calumet. Don't discount the 10d, 20,d and 30d either. Just because canon's put out a new camera every year in the d line, it doesn't mean avoid the former. These are all great cameras, feature packed and can be had pretty cheap since everyone jumps on the " I gotta have the newest technology " bandwagon. (self included).
Powers also very correct in stating "The glass is where it's at". I won't get into costs, I've got enough money in top end glass to build a motor for my car. Just remember that the reason lenses are more expensive is because of their ability to work in tough lighting environments. Fast glass, superior optics, and build quality are the three main things your paying for in those big end lenses.
