It appears that the next lens that Sigma plans to release appears to be a 24-105mm F/4 DG OS, at least if you put any stock into rumors and the leaked images below.
According to a post on Canon Rumors, the rumor site received the leaked image along with a tip that the lens will be announced sometime here in the next 6 weeks or so. As with any leaked images there is the possibility that they are fakes, but the images that I have seen here seem to pass the eyeball test.
The rumor also states that the lens will be a bit bigger than the current Canon 24-105mm F/4L IS. The new Sigma lens will have an 82mm filter thread, weigh in at 885 grams, and will contain 19 glass elements in 14 groupings.
It will be interesting to see if this lens does get announced how it will compare with the Canon 24-105mm F/4L IS in terms of performance, build quality, and of course price. If Sigma’s latest run of lenses is any indicator I think it is pretty safe to say that the Canon will have its work cut out for it on all three fronts.[via Canon Rumors]