Tamron EF 24-70 f/2.8 VC
Don't want to wait for the new Canon EF 24-70 f/2.8L II? Don't feel like spending $2200? Wanted some form of image stabilization, perhaps the new Tamron 24-70 f/2.8 VC is for you.
Quick MTF Review
Roger at Lensrentals.com also did a quick and dirty MTF comparison between the new Tamron 24-70 f/2.8 VC and the current Canon EF 24-70 f/2.8L. The Tamron faired quite well.
Roger also mentions the autofocus performance is pretty good on the Tamron, maybe not as quick as the Canon, but much faster than Tamron's 70-200.
You can read the entire quick and dirty review at LensRentals.com here.