1. EOS 550D / T2i with 18 Megapixels to 15.1 on the 500D / T1i 2. 550D / T2i offers 720p at 50 or 60fps or 1080p at 24, 25 or 30fps,500D / T1i offered HD at either 720p in 30fps or 1080p in 20fps 3. Both cameras feature 3in high resolution screens, but the 550D / T2i's has a wider 3:2 aspect ratio which matches the shape of the images http://www.cameralabs.com/reviews/Canon_EOS_550D_Rebel_T2i/verdict.shtml