Dark Souls is 20% off on GMG with discount code: O3H7FE-D4NFO0-F0LIGK
That brings the price to $40USD for those interested.
For those who don't know, GMG also has a Playfire service, where you can link your Steam account and they'll add cash credit to your GMG account for completing challenges.
Challenges are stuff like playing a game for the first time and getting particular achievements.
I've been doing Playfire for the past ~2 weeks and it's how I'm getting Dark Souls II for this price
Almost all the credit is from me just occasionally getting achievements in games the past 2 weeks.
Right now I think they've got offers for a bunch of worms games, Super Meat Boy, and Fez and you can get the credit mad easy.
I probably sound like I'm shilling hard for GMG but it's legit just a superb deal all around and more people need to know about the whole Playfire thing. It's kind of ridiculous how much credit they give out.
Also, if you don't want to actually invest the time in the game, as long as you at least own it, some people have totally used Steam Achievement Manager to just unlock the achievements and get their credit that way.