Today only, Roberts Camera via eBay has the optically-stabilized Sigma 17-50mm F2.8 EX DC OS HSM for Canon for $429.99. They’re an authorized Sigma retailer, and this is the cheapest price from an authorized dealer that we’ve seen since tracking this lens in 2011.
Compare with other authorized retailers who are currently asking $569 for this lens. This lens was due for a price-drop as the Canon equivalent EF-S 17-55mm f/2.8 IS saw a price drop from $1059 to $879 a few weeks ago. At less than half the price, this Sigma version is a fantastic deal.