Ebay... I have a new pair of Oakley Polarized half-jackets that I was going to list.  Bought a pair of half-jackets and a pair of juliets to see what I liked better.  Going to keep the Juliets and sell the half-jackets.

Just make sure you bid on an auction from a reputable buyer with good feedback selling oakley's or whatever brand, email folks who have won other auctions from the same seller for the same item and make sure they get an authentic product.  You can save 25-30%.