Sigma USA authorized dealers via eBay has some great deals on Sigma lenses for Canon mount.
Sigma 18-35mm f/1.8 DC HSM Art Lens – Open Box – $699.99 – at Cameraland via eBay.com (Compared to New at $799)
Sigma 50mm f/1.4 DG HSM Lens – $399.99 – at Cameraland via eBay.com (Compared to New at $499)
Refurbished Sigma 18-250mm f/3.5-6.3 DC Macro OS HSM Lens – 4 Year Simga USA Warranty – $249.00 – at Buy Dig via eBay.com (Compared to New at $349)
Note: Camera Land and Buy Dig are both Sigma USA authorized dealer, you will get warranty from Sigma USA.