The Sigma 18-35mm lens was famous from the moment it was announced. How in the world could Sigma create a zoom lens with a f/1.8 aperture and still retain image quality? Well, they did it, and today the lens is the lowest price we have ever seen.
Keep in mind that this lens is a crop sensor lens meaning that it will not work with full frame Nikon or Canon cameras but will work well with APS-C cameras. This lens is also a favorite amongst micro four third shooters. By simply adding a Speed Booster to your M4/3 camera, you can get an equivalent 25-50mm f/1.2 lens which is simply unheard of. This deal currently includes both Canon or Nikon mounts and is being sold new, from a Sigma authorized seller with full warranty. You won't find this lens any cheaper.
Update: They sold out but you can still buy it on B&H