Fantastic choice, this lens is meant to be one the best 17-50 2.8's around at the minute! Just check the reviews, if you find a bad review then show it to me. I've seen great reviews across the board, it isn't CHEAP though sadly!
I have used this lens with a Canon mount. It has a respectable image quality and above average build versus most consumer lenses. The Tamron 17-50 has a good following too and is over $100 cheaper for the non-IS version and just a tad bit more than the Sigma for IS on B&H right now.