Those GMG vouchers don't only work on Dead Island...

All those threads telling you how to get Dead Island for cheap never explicitly mention this... But most of the games on GMG can use the 20SUM-MERSA-VINGS or 20PEC-FACEB-SAVER or 20PEC-TWEET-SAVER codes...

All of them give 20% off (only one can be used per checkout though.)

The thing to keep in mind though, is that if it doesn't say ON THE STORE PAGE for the game you're buying that it needs steam, then the key won't work in steam.

The easy way to find the games that can be activated in steam is also really simple. In the search box on the top-right of the GMG site, type (without quotes) "steam". that should show about 10 pages of games that can be activated within steam, and at least one of the 20% off codes should work for them (I think you can only use each code once though, so if you want a lot of games, be prepared to buy them all at once.)

Some of the games that use steam are:
Deus EX:HR (and the augmented edition.)
Dead Island
Red Orchestra 2
Total War: Shogun 2
Just Cause 2
F.E.A.R. 3
and a lot more

Now, I admit that most people could assume that the codes could be used site wide, but I still wanted to make sure everyone knew about it. That, and it also gives me a chance to post my referral link so I can also get some awesome games (hopefully)

my link
and for people who don't like using the referrals (although it helps you too.)
non-referral link

Anyways,
Happy Gaming!

P.S. For any of you guys who really like zombie games, there's another deal going on here greenmangaming.com/zombies/
that has all the details. Have fun!