I'm going to be that guy who recommends 3rd party glass. If you REALLY feel you need an upgrade in the 70-200 range, I've heard Tamron's new 70-200 f/2.8 VC is outstanding, and in your price range.
That said, I'm going to stick with the others in recommending that you get faster glass in the WA to normal range seeing as you'll be using it more. As a 24-70 consideration, once again, Tamron's 24-70 VC (which I own, and love) is actually sharper that canon's mark 1 and has VC, which you may enjoy. Otherwise, you might want to look at Canon's 16-35 (or wait for it to be updated) and Tokina's 16-28 f/2.8, which is said to be an incredible lens for the money (although it won't accept filters). I own one of Tokina's APS-C UWA lenses, the 11-16, and especially from f/8-11, it's a great value.