If you can only have one multi-purpose lens for the 5DIII, the 24-105 would have to be it. It's probably the best standard zoom combination ever made for any format, ever. Yes, it'd be nice if it was faster, but it's got a fantastic focal length range, image stabilization, and awesome optics.
As has also been mentioned, the original non-IS 70-200 f/2.8 is another superlative lens, probably second only to the new IS version amongst telephoto zooms.
You might also want to put some thought into your preferred holy trinity of primes. You could do a lot worse than to get either the 28 f/1.8 or the 35 f/2 plus the 50 f/1.4 plus either the 85 f/1.8 or the 100 f/2. It depends a lot, of course, on what, exactly, you're shooting as well as your style.
Cheers,
b&