Can you sell Steam codes on Ebay?

I was wondering if I would be able to sell a Steam code on Ebay or even Amazon? I just bought a new graphics card for my pc, and it will come with a free code for Batman Arkham City.

are you sure its a steam code? Arkham City doesnt have Steamworks. Its a GFWL game.

either way, if its a cd-key that you get, then yes, you can sell it wherever. What you are NOT allowed to sell is a steam gift because it goes against Steam's policies. Even so, some people do it anyway.