How fast and how far do you want it? If you just want a short telephoto, the 135 mm has an aperture of f/2.0 but I don't think you can get them with IS. The 100 mm f/2.8 macro lens does have IS.
You can get the 200 mm f/2.8 without IS and the 200 mm f/2.0 with IS and a lot more $$$$.
There's also the ubiquitous 70-200 mm f/2.8 zoom that has IS.
a canon 70-200mm with IS would give a lot of versatility over a prime, especially since most of the primes that would be cheaper dont have IS with the exception of the newer 100mm 2.8 macro. youll be paying a pretty penny for the 70-200mm though. they have a newer version of that lens that is near $2,500.00. B&H still has the older 70-200mm 2.8 IS USM (version 1) in stock for $1,899.00.
i wasnt too thrilled about getting the 24-105mm f4.0 IS that came on my 5DmkII but i have to say that it is a pretty nice lens for video and the IS on it makes a big difference over lenses without IS. the only thing is being f4 doesnt get you real shallow unless you back up and zoom in then the OOF area is very nice. i wouldnt consider this "fast" though but then again...its not slow either like a lot of cheaper lenses that are @ 5.6 after you zoom in.
I have the Canon 70-200 2.8L II IS and it's pretty amazing. Can easily go hand held at 200mm with only the slightest floating motion. However it's bloody heacy and also perfrms ok, but not as well when you are following something.