I would recommend Richard Osterlind's Principles of Mentalism, as well as his website. Good prices on his products... As someone who used to deal with textbooks professionally, I can tell you that neither Annemann or Corinda are good "textbooks". I wish people would quit recommending them. Oh, and one more thing about mentalism books/products: they're comparatively more expensive than other kinds of materials, generally speaking. Can you find a $10 mentalism effect that will work well for you? Sure. I've got a couple of real winners from Banacek and Dan Harlan that were not expensive at all. Shop around, ASK around.
Here's another important factor, maybe THE most important one: What are you like as a person? What do you bring to the presentation of mentalism that reflects who you are? Eugene Burger said that trying to create a persona to use as a magician is a bad idea. It is even more true in mentalism. I tend to be a high-energy performer, and I don't think that is necessarily the best element for a mentalist's onstage presentation/presence. Thus, when I do stage routines, I choose "lighter" ones that reflect the energy I naturally produce. I also find I can be my energetic self when doing close-up mentalism; lots of good one-on-one and small group effects are out there. And they "play big" when the group is small.
Remember, too, that mentalism works for audiences because the the most interesting topic for people is themselves. HOW you figure out someone's grandfather's name is not nearly as important as the value that person holds for her beloved grandpa. That you know his name brings back all the associations she holds, and you just tapped into HER emotional values. That is the power of astonishment.
