Bryan at TDP has completed his review of the highly anticipated Sigma 18-35mm f/1.8 DC HSM Art lens. His only knocks against it are the lack of OS (which isn't a huge deal) and the limited range on APS-C. However, the uniqueness and performance of this lens should overcome both of those negatives if you're looking for something in that range.
“It is easy to overlook any focal length range deficiencies when getting an f/1.8 max aperture available over the entire focal length range. Not only is this the widest aperture zoom lens, but it is also the widest aperture 18mm lens. Full frame sensor camera owners have typically enjoyed about 1 stop of high ISO noise benefit and background blurring capability over APS-C/1.5x/1.6x format sensor camera owners. But, full frame camera owners do not have a zoom lens wider than f/2.8 available to them. The Sigma 18-35mm f/1.8 DC HSM “Art” Lens is a bit of an equalizer in this comparison.”‘
Preorder the Sigma 18-35mm f/1.8 DC HSM $799 (Coming August 26, 2013)