Obviously, you need some creepy horror RPGs to play this week. The Bundle of Tentacles lets you get entangled by a ropy, squirming mass of them, including Trail of Cthulhu and several Call of Cthulhu supplements.
Bundle of Tentacles is a pay what you want ($7 minimum) collection of RPG PDFs. The base set includes a pair of books by Kenneth Hite exploring the Cthulhu mythos, Cthulhu 101 and Dubious Shards. The star attraction, though, is Hite's Trail of Cthulhu, a Lovecraftian RPG built on the GUMSHOE system. It's an ideal system for investigating the nameless horrors that have crept into our reality from beyond time and space.
Equally alluring/disturbing is the massive and gorgeous Cthulhu Britannica: Shadows Over Scotland, which thoroughly details the land of cold moors and mist-shrouded streets circa 1920 for use in the Call of Cthulhu RPG.
If you pay above the average (currently about $15), you get some bonus books, too. There's another Cthulhu Britannica book about blending British folklore and faeries with the Cthulhu mythos; Eldrtich Skies, a standalone RPG set in the future and pushing the sci-fi angle more than the usual horror; and a variant of the Renaissance Deluxe RPG exploring Lovecraftian horror in late 16th century London.
There are some more bonus books that will be added to the bundle throughout the week, although the shapeless, writhing shadow that just emerged form the corner of my office tells me (in a hollow, echoing voice) I'm not allowed to spoil what they are yet. I can say there are some very interesting books about to be added, ones that let you explore weird and unexpected aspects of cosmic horror.