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gamersgate is pretty good

One of the users here does a thread on Amazon deals.

here http://www.reddit.com/r/GameDeals/

Check bundle sites like Humble Bundle, Groupees, IndieGala, IndieRoyale, etc. too. Mostly for indie games but you can get a bunch of games for a very low price.

Steam. Come mid-July.

Drop down Network at the top and go to the 'Steam Game Sales' website, a few websites are listed there.

You probably already know this, but sites like GMG don't always provide Steam keys. Some games from other sites will require Origin instead or their own personal platform (Gamefly has one and I think GMG's is called Capsule). That might not matter to you, but I'm just throwing it out there in case it does. As far as I know, they'll always specify what platform the game requires, you just have to know to check.

Also, I find this handy: http://www.cheapshark.com/

Russia

Steam, GMG, gamersgate, getgamesgo, bundle sites. That's about it (maybe some others like Nuuvem, too). Do not, DO NOT use sites such as g2play.
Also amazon, Russian and Brazilian Steam.

Kinguin, recently picked up Darksiders for $9 on there.

I'm borrowing your thread. Here is a key B08ZG-A9HYY-7VQG5

steamblackmarket.com

You can join the Trader's Guild steam group for updates on 3rd party steam sales.

you can use borderlinx site to buy from amazon even if you don't live in US

http://isthereanydeal.com/

Join Hookups steam group for daily deals.

http://www.cheapshark.com/

Summer Sale is the place. But Amazon is a great option.

Amazon doesn't allow non-US customers to buy games from them. Which is pretty stupid seeing as their motto says something about being the world's leading videogames seller. Personally I prefer GamersGate, but I wouldn't mind Green Man Gaming either as it has some pretty sweet deals. Good Old Games is another store i would recommend.

http://gamingsrc.net/ sells all the recent humble bundles in case people have missed them which gives them the chance to buy the bundle anyway. If your interested in buying bundles rather than individual games you can check it out.