back to macro, you could also try the 60mm. i had one, again - great IQ and I couldn't detect any difference between the IQ from it and either of the 100's. It's cheaper and makes a nice inconspicuous lens for candid street shots, it's small. I moved to the 100's to get more working room between camera and subject when shooting macro.
Good info. I just thought I would add some information about minimum working distances and such:
Ef-s 60mm f/2.8: 8 inches. (Will not work on Full-frame digital or film bodies)
EF 100mm f/2.8: 12 inches.
EF 100mm f/2.8L: 12 inches.
EF 180mm f/3.5: 18 inches.
It doesn't seem like much difference, but the bugs sure think it is. More working distance also makes it easier to keep your shadow out of your picture when using natural lighting. One more thing about the Canon macros: they do NOT extend when focusing. This IS important.
On a personal note, I went with the 100 f/2.8 for a bit of extra working distance and the fact that I still own, and sometimes actually use, a film camera. It makes a nice LONG portrait lens on an APS-c body. I hear the 60mm f/2.8 focuses faster, though.
