I am looking at this Sigma 18-200 F3.5-6.3 for my Nikon right now.. I have used one on my Bro in law's D200. It covers a pretty good bit of ground. Not too pricey. http://www.adorama.com/SG18200EOS.html
My vote is for the 24-105L as well. Nice weight /balance on a 5D or 1 series, quite a bit lighter then the 24-70. Plus there is something about that 24-70 zooming backwards that I could never get used to.
On a 1.6X sensor the 17-40 is very nice.
17-50 f2.8 efs if you have an efs body.
Sigma 18-200 is relatively sharp but AF's like a dog on Canon bodies.