The Sigma 24-60/F2.8 EX DG is also a good alternative, although not as wide or as long as the 17-70, it is not as heavy and it is constant aperture. And it is a bit less expensive.
The indications are it is being discontinued (though no confirmation) by Sigma in favor of the other lenses in its range. So it is being cleared by many stores. It is listed in the USD240 range. I got mine from Henry's Photo-Toronto for USD238.
Check out the reviews. They report very good IQ. Of course there has been some feedback about BF-FF issues but all the other lenses mentioned have the same thing. My copy is ok based on pix taken to date.
I have this lense as well, and love it. Do a search on this forum if you want to see some sample images.