Having gone with the 24-105mm option, I'd suggest going another route. 15-85mm is a nice lens, or perhaps consider the Canon 17-55mm f2/8 or the Tamron 17-50mm f/2.8 (non VC version).


On the 24-105mm, 24mm isn't wide enough, and I don't find the lens to be super sharp.


With the 15-85mm, you'll get more range on both ends compared to your kit lens (assuming it's the 18-55mm), and it's quite sharp. It's probably quite a bit lighter too.


The Canon 17-55mm is generally regarded as the best general purpose zoom for a crop body. With a constant f/2.8 aperture, you can shoot with thin DOF, or in lower light. It's in the same sort of price range as the 24-105mm.


The Tamron 17-50mm is supposed to be quite a nice lens, plus with a constant f/2.8 aperture, you can shoot with thin DOF, or in lower light. The VC version (Tamron's name for IS) is significantly softer, so you'd be giving up image stabilization if you did this. The reason to consider this vs. the Canon 17-55mm is that it's less than half the price.