I have to agree with Jonathan with respect to the 10-22. Ok its not too bad if you want to go as wide as possible',but I never thought it anything special. Certainly not sharper or a better lens than the 17-85. While the 10-22 was acceptable I have been much more impressed by the 17-85. This is consistent with a number of these lenses I have had a try at or indeed from others I also know who own them.
However unfortunately your not left with too many other options when using a 20D at the wide end with Canon lenses. You'll have to test some other brands to see if you think they perform more towards your expectations.
Other than that you'll have to sell up, get a full frame camera and break the bank for a wide L.
It was always my opinion that combined with the 20D these two lenses however provided a nice overall travel pack with respect to image quality and portability.
I doubt the 50 will get you any better a shot than your 17-85 during the daylight hours. However at night or indoors its a very handy one to have with you.