Have a key for Metro 2033. It's a steamworks game so you will need Steam (if you game on PC and don't already have steam, shame on you) You put the key in to steam and it'll link to your account and download.
Retail on steam is $39.99, I'm asking for $15 or best offer. Thanks.
Some screenshots I took for people interested:
Spoiler: show
More info here: http://store.steampowered.com/app/43110/