DuhJeepster,
I have both extension tubes and a good Canon diopter. Both are useful in certain situations, and actually the combination of both is the best overall situation. Reasoning- with the extension tubes you lose light, and therefore have a slower shutter speed (or less depth of field). The diopter doesn't cause you to lose light, but doesn't get as close either. So the 500D with the smallest extension tube is just about perfect for 3-4" focusing distance on a 135mm non-macro lens. I haven't tried the 500D on my macro yet because I lost my step-up ring, but I'm guessing I'll be able to get right up to the glass without an extension tube on the 100mm macro with a normal minimum distance of about 12".
EK- not sure about camera exchange for one thing, but you can get a Canon ef 100mm f/2.8 USM macro for about 460, a little cheaper without the USM (which is kind of worthless with macro shooting anyway). The next step up would be the 180 mm L series (i.e., professional grade) macro, and $1500 for that doesn't sound off base. Other good macro lenses for a canon SLR include the Tamron sp 90mm macro, which I hear is almost as good or equally as good as the canon macro for about $20 cheaper, but you do run the risk of compatibility issues down the road. Also, Sigma just came out with a 180 macro that rivals the Canon L series model, but goes for around $800 IIRC. Skip the Canon 50mm macro, you're better off investing in the 100mm even if you have to save a while longer.
Final point- there is only one (other than Nikon) lens made specifically for a DSLR, and that is the Canon EF-S 18-55mm that comes with the digital rebel. Every other Canon EF lens works equally as well on Film or digital SLR bodies. The only difference, again, is the crop factor of the DSLR sensor- in the case of the 10D and Digital Rebel, multiply focal length by 1.6 for the 35mm equivalent. For the type of photography we do, this crop factor is a huge benefit (refer back to the price of 180mm macro vs 100 macro) until it's time to take a full tank shot. Then you kind of wish you could have a better wide-angle.
Hope this clears up some stuff.
T