Check out Mark Wilson's Complete Course In Magic. It's basically a magic textbook, and it has a whole section devoted to the double-backed card. It also talks about double-faced cards, short cards, short-cornered cards, a plethora of card sleights. . . and that's just the card section. It goes on to coin magic, bill magic, silk/handkerchief magic, etc. I've found some real gems in that book, and there are some really strong double-backer routines.
The first time I got it was at my public library, but I think some bookstores have it. My copy came from Barnes & Noble, I think.