Not sure if you already are, but if you're a Canon user I would strongly recommend joining the
POTN forum. It's almost a must for learning about your gear, reviews of gear, getting help using it, getting opinions on what lenses to buy etc. Not just lenses - bodies, flash, tripods, other accessories. Also posting images and critiquing for improvement. Very similar setup and use to this wonderful forum, and the mood is most friendly. Can't recommend it highly enough. (Dave, I know your view on POTN is somewhat different, but I'll stand by what I say above for Chris' situation
)
Sigma do make great lenses. Sorry to hear about your bad experience. I'll echo the advice of others above.
There are plenty of "dud" Canon lenses out there too, and Tamron, and Tokina.
Whenever I'm contemplating a new lens purchase, I trawl POTN and dpreview for reviews and comments on them. You will get good and bad reviews on anything.
PS - Dave, "OS" is Sigma's equivalent of IS (image stabilisation)