Look
Here and see what you think.
Handle both cameras and see which one you think youll not tire of easily . I was in exactly the same positon as you and bought the 350D + camera grip + extra battery and now going for some lenses.
The PQ is very similar. What you pay for ( apart from the Pose factor: My camera is bigger than yours:

) Is perhaps a percieved ruggedness, durability and a tangible responsiveness said to be better in the 20D.
With the benefit of hindsight ,I still feel happy that I did not buy the 20D( for the £400-500 difference then) because Im now looking at the 30D, 5D or even D200 Nikon as possible upgrade paths only 12- 14 months after!.
If the cost difference is less now you may be swayed