Basically if a really good game you recommend is on a daily deal or a flash sale(cheapest it can get) post it. also general good sales post i'll start: papers please for 5$, real good game. fez for 2$ is basically a must-buy, amazing game and that's dirt cheap
rebirth for 7$ is really, really, worth it if you like the type of game, bought it for 15$ and i have 200 hours in it
Ziggurat a pretty decent game I'd also recommend Darkest Dungeon, although it's only 25% off, they just added some new stuff GTA V is like 56 euros, the sale is mostly for the franchise.
monaco is 90% off so i'd recommend picking it up in a group magicite is 3.5$ and I heard it's pretty good surgeon simulator is 2.5$ and that's pretty nice aswell.
Victoria Collection for a 10 EUR is really good, especially if one likes grand strategies, one of the best Paradox titles I've heard good things about Long Live The Queen too, it's a steal for bit more than a euro. I myself really enjoy The Guild games so I'd definitely recommend picking the collection up for 3.74 too.
Chivalry Medieval Warfare for £2 is a sweet deal. The Evil Within is around £9 right now as well, which is a little bit of a steal as well
But first you need to watch a tutorial on how to stop it being locked at 30 frames a second and to get rid of the black bars.
You can get yesterday's deals for the same price next day. Luftrausers 2.49 EUR - fucking awesome game. How To Survive 0.69 EUR - it's a decent isometric view single player survival/crafting/zombie game. Civilization franchise.
Far Cry 3 at £3.74 is another singleplayer game I highly recommend (never tried its multiplayer personally) Big +1 to Civ franchise too
Tales of Maj'Eyal - 1.19 EUR - great roguelike (I don't remember exactly but you can get the engine itself for free and maybe the game too, but this version has some additional stuff) Ryse: Son of Rome - 13.59 EUR - I enjoyed this game, the combat system is not overly complicated but kinda a breath of fresh air, the story is decent too.
I highly recommend SpeedRunners. It's so much fun with four players. It's on sale for another 7 hours: http://store.steampowered.com/app/207140/