Shadowrun is a fantastic source of ideas, particularly if you go for a less scrupulous group of heroes or a more mercenary campaign setup. Works really well in Sharn (Eberron).
Of course, you have to steal any and all H. P. Lovecraft-related material you can. Done well, it's a great addition to any campaign.
The X-Files had more good plot hooks than I can count. Same with any modern conspiracy/horror movie or video game (Silent Hill, Resident Evil, Dog Soldiers) and classic horror flicks (The Thing, Halloween, The Howling). Several sci-fi movies & shows work too (Aliens, Pitch Black, Battlestar Galactica).