I think the 24-105mm f/4L IS is an excellent lens - the ideal general purpose zoom for full frame, but a nice outdoor walkaround lens on APS-C as long as you don't mind that it normal-to-tele and lacks the wide angle focal lengths (pr maybe you have an APS-C ultrawide zoom to cover that). I do agre with Rick that the EF-S 17-55mm f/2.8 IS is the best general purpose zoom for APS-C.
I'd not wait for a MkII of the 24-105 - the current lens is the kit lens for the 5DIII, meaning it's likely to be around in it's current form for some time, and a new version will certainly be a lot more expensive if Canon's recent trends are any sort of guide.
You might consider buying a resold new copy - especially with the 5DIII coming out, a lot of people who buy a 5-series body buy the 24-105mm lens too, and sell it new in the white box. The lens adds $800 to the kit price, so they're commonly sold for ~$900.