I have a D80 myself and I love it. I had the same debate btw the Nikon and Cannon when I was looking into DSLRs. I picked the Nikon, over the Cannon after holding it and playing around with it a bit. It just felt better to me personally. My friend did the same thing, but went with the Rebel XTi instead.
Both Cameras take awesome pictures. The only thing was from what I saw, the Nikon entry level cameras tend to be more expensive than comparable models of the Cannon DSLRs.
Else off the top of my head I remembered from my research:
Rebel XTi - was faster in taking pictures (per second); and had an internal dust repellant/cleaner. Colors are very crisp, but not as accurate as the Nikon.
D80 /D40 - Colors are suppose to be more accurate (but you can adjust on all the DSLRs), better pictures at higher ISO also.
Sony -- vibration reduction on the body - thus you dont have to spend extra money on the fancy vibration reduction lens like if you have a Nikon. However, Cannon and Nikon have a lot more accessories and lens for their DSLR/SLR than Sony has for their line of DSLR/SLR cameras.