I was watching a workshop the other day, and the professional photographer mentioned that 9 times out of 10, he suggests buying a better lens than a better body.
One of the main reasons is retention of value, but the other reason is you can get better images with great lens and an ok body, versus an ok lens with a great body.
For video I recommend either the 24-105mm f/4L or the 17-40mm f/4L. The only reason I say this is because don't most videographers use smaller apertures (I think)? Why spend the extra money for f/2.8 if you don't need it?
For photography, I recommend either the 24-105mm f/4L or the 24-70mm f/2.8L mainly because those two are more versatile than the ultra-wide-angle 17-40mm f/4L for a variety of shooting styles.
Since it looks like the 24-105mm f/4L is the least common denominator, I would choose that one. Plus, you'll save ~$400 over the 24-70mm f/2.8L, and I've heard it's harder to find a really sharp copy of the latter. Additionally, the latter has a Mark II out soon for $2300, which is uber-pricey.
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