From Hugme.org

Camera-Compare:Canon 1D-5D-7D-50D-T2i

I hope to be purchasing a new camera soon. I've built a chart to compare some of the canon cameras to help with that decision. I believe I'm going to be going with the 5D

Basics	1Ds Mark III	5D Mark II	7D	50D	T2i
Price	$6,113.95	$2,399.00	$1,599.00	$974.95	$799.95
Resolution	21.1MP	21.1MP	18MP	15.1MP	18MP
Sensor	36 x 24mm	36 x 24mm	22.3 x 14.9mm	22.3 x 14.9mm	22.3 x 14.9mm
Crop Factor	None	None	1.6	1.6	1.6
Lens Type	EF lenses ONLY	EF lenses ONLY	EF or EF-S	EF or EF-S	EF or EF-S
Shooting Information
Sensitivity	100-1600 (50,3200)	100-6400 (50,12800,25600)	100-6400 (12800)	100-3200 (6400,12800)	100-6400
Burst Capability	High:5fps Low:3fps	3.9 fps	High:8fps Low:3fps	High:6.3fps Low:3fps	3.7fps
Flash	not built in	not built in	Pop-up	Pop-up	Pop-up
Viewfinder/Display
Viewfinder Coverage	100%	98%	100%	95%	95%
Power
Battery Type	LP-E4	LP-E6	LP-E6	BP-511A	LP-E8

The 5D and 1D cameras are both full frame cameras. Notice the size of the sensor is much larger. This is the biggest difference in the cameras. the 7D,50D and X2 are made for the EF-S lenses too. They don't perform as well with the EF lenses, you get a much smaller view. All but 1 of my lenses are EF, The one EF-S lens I have will not work on the 5D as full frame cameras can't use them. When I sell the camera I will just include that lens. It's sad because it's a lens I really like. I'll just have to find a similar one I can use.