I would like to post every special offer or hot deal for games on PC in this topic so that we can play great games on our computers as well as save some money.
http://store.steampowered.com/ - Of course Steam should be your very first choice. Unlimited store, a pretty light client, server availability for multiplayer gaming with an anti-cheat system. Games are automatically (and regularly enough) updated and you can also play in offline mode. You can login into your account on any PC and many games have a cloud storage system so you can play on different PCs but with all your savegames. Obviously, you cannot login on multiple PCs simultaneously. A piece of advice: never buy full-priced games; just wait for the Summer, Halloween and XMas Sales and you will get outstanding games at awesome price. Every day there is special deal and every week features the "Midweek Madness". Plus, you can play a multiplayer game for free on weekends to try it out.
http://www.gamersgate.com/ - There is a UK version of this too, so check it out before you buy something from either one because the price could be lower on the other site. Pay attention to weekly discounts because there could be some good stuff on sale. As far as Steamworks or Origin games are concerned, you are immediately given the activation key.
http://store.origin.com - Well, Origin is EA's stuff. Way worse than Steam but it is getting better. Anyway, they too often got pretty good deals. For instance, I just bought Mirror's Edge at 1.47€ (about $2) and Tomb Raider 2013 Survival Edition at 7.49€ (about $10). Check it out.
http://www.greenmangaming.com/ - Useful site, always keep an eye on this one.
http://www.impulsedriven.com/ - Gamestop's online store.
http://www.gog.com/ - Good Old Games and more. Neat offers, free DRM and loads of extra.
http://www.hotukdeal...aming/deals/hot - Users here write real-time alerts about hot deals. Be careful, some offers are only available in the UK.
If you are into indie games, you should take a look at this sites:
So, if you are interested in this stuff, we can regularly update this topic with the new deals available.
Witcher 2 Enhanced Edition at 50% off (€9.99 - 13.53$) on Origin
Thief at 50% off (14,99€ - $20.31) till Monday 10am PDT on Steam
Complete GTA Bundle (III/Vice City/San Andreas/IV/EFLC) at €9.99 - 13.53$ on Green Man Gaming - 24hr deal