The Japanese photography blog Egami wrote about two Sigma patents about a week ago: one for a 16-50mm f/2.8 standard zoom lens and another for a 12-24mm f/2.8 wide angle zoom lens for the APS-C format. The applications for the patents are said to have been filed in October 2012, so if these lenses are in fact being developed and the patents have not just been filed for protection reasons, they should soon be ready for the market. That is, as always when we’re talking rumors and patents, a big “if”. In the same post on Egami you can see that Sigma has patented the designs for the 18-35mm f/1.8, 15-30mm f/1.8 and 17-35mm f/1.8, of which only the first has been launched. Below you can see the optical construction of the 12-24mm f/2.8. If I haven’t counted wrong, it is made up of 17 lenses or “elements”, which is significantly more than other 12-24mm zooms have. The Nikon, for example, has “only” 11 lenses.
The same entry linked the following blog post, which claims that at a 50mm f/1.4 “adventure event” an announcement was made that an 85mm f/1.4 is also currently being worked on.