ok, i just read through this thread and the other
I'd like to point out that EOS 550D shoots videos in
•
1920 x 1080 (1080P, 16:9) @ 30/25/24 fps
• 1280 x 720 (720P, 16:9) @ 60/50 fps
• 640 x 480 (4:3) @ 60/50 fps
• Quicktime MOV format (H.264 video,linear PCM audio)
•
Up to 29 min 59 sec (or max file size 4 GB)
EOS 550D shoots in 1080p not 1080i. Canon EOS 550D / Rebel T2i Review: 2. Specifications: Digital Photography Review
while Nikon D90 can only do
Nikon D90 Review: 2. Specifications: Digital Photography Review
•
File format AVI (Motion-JPEG)
•
Image size (pixels) 640 x 424; 24 fps 320 x 216; 24 fps 1280 x 720; 24 fps
• Compression: Motion-JPEG Audio Monaural on/off selection
• Exposure: Determined with matrix metering utilizing output from the image sensor
• Exposure lock available
• Exposure compensation available in P, S, A, M modes
•
Maximum single clip length: 1280x720/ 5 minutes, others 20 minutes
If you're seriously considering to use dSLRs for video then the file format is not an issue really. I can find so many applications in the internet that can let me convert the MOV format into something "native" for well known video editing applications like sony vegas for example.
So in terms of video, and ONLY IN VIDEO, it's obvious who the winner is - CANON EOS 550D!


In terms of photos, well, the Naykon D90 still has plenty more to offer than the EOS 550D. Read here:
Canon Rebel T2i / EOS 550D Compared to the Nikon D90 Side by Side