Hmmm...I have my eye on a Canon XTi... I think the difference between the basic Canon and Sigma lens would be mostly cost. Now..Canon makes the "IS" lenses for the Rebel XTI which stands for image stabilization...this is what I want. It makes a BIG difference in the quality of your pics, especially when shooting with a zoom lens and at night / low F-stops / etc. It's like having a tripod built into the camera..put it that way. Of course these lenses are much more costly than your standard lenses...and the Sigmas are not IS lenses as far as I know.