A friend of mine has the Rebel XT amd I have the 20D. I must say that the images taken by these cameras are very similar. The biggest differences are the other functions of the cameras. Like the 20D has a higher FPS (frames per second) capability is higher, there are more custom functions, the metering and focusing systems are arguably better, and body seenms more durable. Plus, it feel bettter in te hand. That said, and assuming you don't need the extra bells/whistles on the 30D, I would buy the Rebel XT and couple it with better lenses such as the 17-85 IS or (what I use) the 17-40 f/4.0L lens (the best I've used). Then pick up a Sigma 10-20mm wide angle, and a Canon 70-200 f/4.0L tele lens. This would be a rather expensive outfit, but would provide you with all the lenses you need.
Being unable to predict the future, I have been staying away from the EF-S dedicated digital lenses. If you buy a full frame camera in the future, or own a Canon film camera, these lenses won't work. The 17-85 IS lens mentioned above is an EF-S lens, but it is very nice and so I recommend it anyway.
Hope this helps. Just remember that as many photographers there are, the same number of opinions will be offered. The above system is just one I've had excellent results with.