BuyDig via eBay offers the Sigma 17-50mm f/2.8 EX DC OS HSM Lens for Nikon, model no. 583306, or Canon, model no. 583101, for $429.99 with free shipping. That's tied with our mention from last fall as the lowest total price we've seen. (It's a current low by $139.) Features include FLD glass elements, anti-shake, 11" focus, and 1.5x magnification.

Update: Specs corrected.