redtagcamera via eBay has the Sigma 17-50mm F2.8 EX DC OS HSM for Canon (grey market) for only $249.99.
This is a great deal for this crop-sensor, optically-stabilized lens, which already delivers terrific value. Please note this not an authorized Sigma USA dealer, so you do not get the Sigma USA warranty. However, at this price, you probably can’t go wrong. This lens usually retails for $369.