Or, if you want something like the Sigma, grab an older 17-70 f/2.8-4.5 Macro. That's the one I have, and it does nearly 1:2 macro, focuses pretty well, and is generally shop. Some field curvature, but that's true of all the nicer kit-level zooms. And its pretty cheap, usually can get it in the $200 range. I'll also second the 17-50 f/2.8 from Tamron suggestions, non-VC of course. They can be had in the $250 range I believe.
If you really want stabilization, then the 15-85 is probably the lens to go with. By the time you pay $4-500 for the Tamron and Sigma versions with VS/OS, you might as well get the Canon.