The Canon EF-S 17-85mm f4~5.6 IS USM was announced in August 2004 as general purpose zoom for Canon digital SLRs with EF-S lens mounts; compatible bodies include the EOS 300D / Rebel, EOS 350D / Rebel XT, EOS 400D / Rebel XTi, EOS 20D and EOS 30D. EF-S lenses are not compatible with the EOS 10D, nor any Canon bodies with larger sensors including the EOS 5D, 1D Mark III or 1Ds Mark II.
The Canon EF-S 17-85mm delivers a 5x optical zoom ratio with an equivalent focal range of 27-136mm on a 35mm or full-frame body. This offers both wide angle and reasonable telephoto coverage, and a more useful overall range than the budget EF-S 18-55mm kit lens commonly bundled with compatible bodies. The optical construction consists of 17 elements in 12 groups. The EF-S 17-85mm also features Image Stabilisation facilities which claim up to three stops of compensation against camera-shake. Read the whole review here