The new Sigma 17-70 2.8-4 C is supposed to be a good lens, tested great at SLRgear.com. About $499. If you need constant 2.8, the Sigma 17-50 2.8 OS is very good, rivals the Canon 17-55 IS for less money (I know, I had 2 17-55 IS copies, and traded the second one for the Sigma 17-50 2.8 OS).
If you look at he way you shoot and find that you hardly shoot below 24mm (which I doubt), then you can actually consider any 24mm-...mm zoom too, especially if maybe you think about going FF one day.
The Tamron 24-70 2.8 VC is a very good lens, excellent value, it's on sale right now on Buydig, but I'm still not sure that it's the best option for a crop sensor body.