My parents want to buy me a new camera for Christmas and I just want to pick the one that's better for the buck. To me, I don't really think the extra 2.1 megapixels is worth the extra $200+. Its main use would be airshow pictures, with a new 300mm telephoto lens.

XTi - http://www.usa.canon.com/consumer/co...&modelid=14256

XSi - http://www.usa.canon.com/consumer/co...&modelid=16303

Instead of those, get them to get you a 40D. Its 10.1 MP but the frame/shutter rate is a lot faster than those two cameras and pictures will be that much sharper.

Otherwise, if you have to select between those two, go with the XSi. It has other advantages/upgrades than just the 2 MP.