This is the Sigma 12-24mm f/4.5-5.6 II DG HSM (available for Canon and Nikon Digital SLR cameras):
Reviews
Review and full-sized, full-resolution photos at Impress (in English) – The Sigma 12-24 II was tested on a Canon 5D Mark II.
Resources
Official Sigma 12-24mm II page at Sigma Corporation of America and Sigma Corporation (Japan).
Related
Sigma Lenses – Main page
Canon Lenses – Main page
Nikon Lenses – Main page