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.
“There is no such thing as a weird human being. It’s just that some people require more understanding than others.” - Tom Robbins