Edit: http://www.minerwars.com/SteamKeys.aspx Apparently its one of those games where they have a separate login thing you have to create. Anyway once you do, you can get the actual steam key there, after entering in the key from GMG.
Just picked up Batman Arkham Asylum for $3.74 with that code.
"We choose the right to be who we are. We know the difference between the reality of freedom and the illusion of freedom."