I think I found this on DPReview.com, posted by someone in a comment thread. Maybe this isn't very groundbreaking, but there's a (brief) history of the Sigma brand from 1961 to 2011. It's not as complete (nor as slick) as the Canon Camera Museum but I've found this page to be quite enjoyable. Many (though not all) lens/camera names are clickable, leading to sub-pages describing the relevant product. Some pages aren't working fully or are missing images though, presumably due to being out of date.
This answered a few questions of mine - say, in which year Sigma has introduced HSM lenses, or how old is my 14/2.8 lens (turns out it was introduced in 1998 and was one of the first "crinkle finish" units, as well as one of the earlier HSM units, even though there had been HSM lenses with "Zen" finish like the famous 300/4 and 400/5.6.
The Global Vision era is not covered - but it's pretty well documented anyway. It's the "Dark Ages" that look the most interesting to me.