For the Canon camera, I would suggest the same as sweet ride, to go with the 100mm f2.8 usm macro lense.
I bought mine used off of ebay for $400 shipping included and I am super happy with it.
I don't have near the photography skills as sweet ride, but the type of shots you can take with it are just amazing.
Here are a few of mine.
The little 58mm screw on macro lenses +2 - +10 work more like a magnifying glass and while you can get a little close up, you don't get nearly the depth of field nor the clarity a true macro lense gives you. I tried them. You can get them for around $15 on ebay.
I have also heard great things about the sigma 150mm f2.8 macro lense though I have never used it.
Also might I suggest when you do get a good macro lense, to get a tripod and a remote shutter as this will greatly reduce camera shake making your pictures much sharper.