PopPhoto did a comparison of Nikon D40x, Canon XTi and Sony A100. Here’s the conclusion:

Canon EOS Digital Rebel XTi: With 18-55mm f/3.6-5.6 Canon EF-S lens ($770, street):

The Nikon D40x produces Image Quality a bit higher than Canon’s mighty lightweight, notably in better noise control throughout the ISO range, and it has an ISO 3200 setting, which the XTi lacks. But the XTi remains a potent competitor, with faster and more sensitive AF using a sophisticated nine-point AF array that can track across the frame. The Canon takes a RAW file simultaneously with a highest-quality JPEG, not lowest. While we’d rate the build quality about equal, we’d trust the Canon more in dusty conditions, as it has both self-cleaning sensor and software dust deletion (the D40x, just the latter). And the Canon has no AF lens limitations — all EF and EF-S lenses have built-in focusing motors.

Sony Alpha 100: With 18-70mm f/3.5-5.6 Sony Zoom DT lens ($710, street):

The Sony’s singular advantage over both the Canon and Nikon models is its sensor-based Super Steady Shot system, which provides image stabilization across both the Sony and the discontinued Konica Minolta Maxxum lens lines. Canon and Nikon make you pay for stabilization with every lens. The Sony has faster and better-tracking AF than the Nikon D40x, a self-cleaning sensor, and innovative dynamic-range controls. We also think it’s a better-built camera than the D40x. The Nikon wins on Image Quality, with somewhat higher resolution but, more important, clearly superior noise control. The Sony lens line is smaller than Nikon’s AF-S lens catalog, but not by much.

Website : Nikon D40x Compared with Canon XTi and Sony A100