Sigma 70mm f/2.8 EX DG for Canon EOS Digital SLR

Great lens, optically and mechanically.

Optically, the test at slrgear says it all, it's possibly the sharpesst lens available, sharper than the Canon 100mm macroor the Zeiss 100mm. It's so great that I want to buy a better flash to be able to use it in interiors at all times (f 2.8 is not enough for dimly lit rooms and the popup flash can give ugly shadows and some redeye). The focusing is also very accurate, and because of the sharpness of the lens this is very easy to test on real photos, you can see exactly where the plane of focus starts and where it ends. If you were careless with your focusing, it becomes obvious at 100% magnification.

Mechanically, it's well built and it has a very smart implementation of focusing path + focus limiter. Let me explain : the lens has a very long focusing path (around 270°, so it sticks out some 5.5 centimeters for 1:1 macro). The AF motor is non HSM, so watching the lens going through all this path is very slow and noisy. But the focusing path is implemented in such a way that normal focusing distances (between infinityt and 0.5m) take up only 40° or about 1cm of lens protruding. So if you use the focus limiter, the lens is very fast and responsive at normal focusing distances. For macro, you can go in manual mode and the long focusing path will let you make very precise focusing. It's really a very well thought out lens.

The only disadvantages are that it has a minimum working distance of only 7cm at 1:1 (decent, but more is usually better here) and that it partially blocks the popup flash for 1:1 macro, so you can use the built in flash for macro photos only until 1:1.5 maginification (that's still very well for crop camera users who don't want to buy a dedicated ring macro flash).

See a very good test here :
http://www.slrgear.com/reviews/showproduct.php/product/964/cat/30