Steam have a Halloween sale on, until 31st October (obviously).
There are a couple of dozen games on sale, with the likes of Left 4 Dead, the two Bioshocks, the Dead Space games, Resi Evil 5, Overlord 1 & 2, DMC 3 & 4, Ghostbusters (and Sanctum of Slime), Dead Island, Plants vs Zombies GOTY, Borderlands GOTY, Stalker Bundle (Pripyat & Chernobyl), FEAR 3, Silent Hill Homecoming, Dungeons, SAW, Zombie Shooter 1 & 2, Zombie Driver. There's also a pack for Train Simulator 2012 (aka Railworks 3) - Trains vs Zombies ... just to prove that you can put zombies into any type of game ...
There are a few other more unheralded titles too - indie titles such as Chthulu Saves the World & Breath of Death 7. I'm wondering whether to get hold of Vampire: The Masquerade - Bloodlines, a vampire RPG/FPS based using the source engine.
Amnesia: The Dark Descent is there for £2.60 - I've only played it for a couple of hours, but it did succeed in putting the willies up me (gotta love that phrase). It's particularly effective because you're not armed, which ratchets up the tension a fair bit.
Soon you will have forgotten all things: soon all things will have forgotten you. (Marcus Aurelius, Meditations, Book 7)