I am still a proud user of a Canon 20D. I will start off by telling you that it is still a perfectly capable camera, a camera that I would choose over any of the X00/Rebel series cameras to this day. I have used the Rebel XT/350D, t3i/550D, 60D and the pro orientated bodies like the 5D, 5DII, 5DIII and several flagship cameras I still feel that if I were to choose a camera I would look at the older bodies like the 20D, 30D, 40D and 50D. Those are cameras that were released before a shift in Canon's line-up that saw the X0D line turn into an enthusiastic amateur line-up rather than prosumer.
To get the kind of camera that was offered in the 20D in the current line-up you'd be looking at the 7D.
Here's a comparison of the 20D with two more modern EOS bodies, the t2i and 60D. Unless you want video or to crop your images massively then the 20D is just fine.