I'd have to say (other than the Player's Guide and the Marshal's Guide) the books I use the most are......The Great Maze box set, Law Dogs, Hexarcana, and a variety of Dime Novels. Depending on what type of characters are playing, you can't go wrong with Hucksters and Hexes, Fire and Brimstone, Ghost Dancers, Book of the Dead, and Smith and Robards.