Any of the current offerings are so much nicer then the 10D in so many ways just pick something and go with it. Have you tested the 20D and 30D or used them at all? They're a LOT better then the 10D. I say that as a former 10D owner. There are numerous situations, lighting conditions, etc.. the 10D could really fall on it's face and the 20D/30D shot would simply be head and shoulders better, and allow you to get the shot with significantly less fiddling with the camera and so on and so forth.
Metering, dynamic range, speed of operation, ease of operation, battery life, autofocus, software, noise, etc.. are all improved a great deal on both the 20D/30D and 5D versus the 10D.
I have not tried the 350D or the 400D but IMO the image quality on the 300D was slightly better in some ways then the 10D, so even a 350D or 400D should be a noticeable upgrade for you.
It sounds like you just don't really want to spend the money on a new camera. If that's the case fine, if you do want a new camera, you're going to be very happy with any one of the current cameras.