One thing to consider is that there /might/ be another XXD camera coming out very soon.
If the video is important, the new camera might have it. However, being new it will cost
If cost is important, the new camera might make costs lower.
Have a look in the 50 owners thread. A poster has put up a very good selection of images, taken at different ISOs with the 50d. Makes me drool over the 50d and wanting to get rid of this 400d soon.
Just got a 100-400L this afternoon, thanks to someone on here. And a quick test shot shows how much difference good glass can make.
This is a hand held, 1/20th s shot from the camera, measured at 8m distance, and the area of the shot is 1 inch high.
None of my other lenses come close to the resolving power of this (and by that I mean the unblurred quality)!
I was shocked when I saw that I could see this from there....
Good lenses make a world of difference!!! (I already have the 28-135 IS, 75-300 IS, both good lenses, but not of this quality!)
Edit: should say that this is a 100% crop, this part of the image is 368px x 250 px out of ~3600x2500, i.e. 1/100th of the whole image!