From my experience, (whatever that might mean to you,)
I find that books written by good magicians or mentalists tend to be a lot better than the bunch of litttle gimmick tricks, (which sometimes cost the same amount).
However i want to read what others have to say on the matter.
Shhh... the use of actual books vs. buying tricks or a DVD is one of the biggest secrets to the whole business. Especially the older books such as Tarbell and some of the old manipulation series manuscripts released by Irelands (Magic Inc in Chicago).
Let's keep this a secret in that people tend to get far more information and effects when they invest into books over that other stuff and it's something the real students of magic don't want all the wannabes to know about... let them keep supporting E, Penguin and all the money grabbers out there
I have learned about 95% of my material from books. Bobo,Gibson, Erdnase, Ammar,Bannon, Corinda, Maven, McBride and Burger, Hikock, Fulves, Wlison, Trost, Zenon, Sankey, Brook, Browninjg, Enriquez, Martin, etc.