I emailed Sigma UK to see if/when there was going to be a Canon version of the Sigma 18-50 2.8 EX HSM, as there is currently only a Nikon version. This is the response I got:
I guess this doesn't mean there will never be a Canon version, but it's not looking liking it's going to be any time soon.
Out of interest, is that true regarding the new Nikon cameras requiring HSM type focussing? Sounds a bit like sales blabber to me (but I stand to be corrected on that one!)