honestly depends on where you live. a lot of my friends are techie nerds so they sell second hand cards pretty often on ebay or amazon but at pretty high prices. Personally I have all the games AMD offer with their cards already so the game codes aren't a huge attraction for me.
You can always hunt down local deals on craig's list or something. or I've been offered decent deals hanging out at microcenter and talking to people browsing the graphics card section