Gerry Morgan , Apr 02, 2009; 11:09 a.m.
I have the Sigma 50mm EX macro and it's a superb lens. In fact, it's the sharpest lens I have. The Canon 60mm is also reported to be excellent. And if the new Tamron 60 is as good as my Tamron 90, it will also be high-performing lens. You might also want to think about the Sigma 70mm EX macro.
If you care about internal focus (lens does not extend when focusing), that would eliminate the Sigmas. But for me, that's not at all important. Given that all these lenses (probably including the new Tamron 60) are wickedly sharp, I would be more interested in looking at the quality of out-of-focus areas (bokeh) and choose the lens that gave the most pleasing (to my eye) blur. It's a very subjective way to choose a lens, though, so you'd need to see sample photos from each.
Will you be using the lens for any purpose other than macro? Portraits? if so, having f/2 available on the Tamron might be useful (for blurring out backgrounds at portrait distances).
If you want full-time manual control (manually adjust focus even when autofocusing), the Canon or the Tamron would be the way to go.
On balance, if I were looking for a macro lens in this range, I would wait until the Tamron becomes available and then look at some sample photos.