The highly rated Sigma 35mm f/1.4 DG HSM A1 ART lens for Nikon mount (see DxOMark test report) is now available for $779 on eBay with free shipping (via 47th. Street Photo). This is a $120 savings over the regular price of $899 (note that this is a brand new lens, not a refurbished product).
Sigma recently announced 4 years warranty on all of their products.
Update: they changed the price and the lens now sales for the regular MSRP.