Yeah, Deadlands because I am running the game in New Mexico I have taken some of the monsters and concepts bringing them into the modern era. I am also using of the information from Boomtown or Bust for some of the history of the area and various towns lost or still in existence today.
World of Darkness: both oWoD and nWoD have some great concepts story arcs and villains to bring in. That is Vampire, Werewolf, Mage, Changeling, Demon, Hunter, Wraith, Mummy etc. I am using the Vampire: Kindred of the East supplement to create my version of the Jade Court.
Call of Cthullu, dear God how can you not?
I am using Legend of the Five Rings, D&D Oriental Adventures and White Wolf's Werewolf: Hengeyokai to create Kitsune. I am working on trying to make them more of Japanese legend not just Werefoxes.