For me, books are more of a reference instead of required material like undergrad. Most of my professors are generally good enough that their powerpoints can be studied from without cracking open a book. However, for really weird subjects embryology, a book might be useful to have.
Though the best advice for most of this stuff is an MS2, 3 or 4. They'll tell you what books are useful enough to buy or not. Oh, and do beware. If you school is like mine, you'll be too bombarded with material and study guides from students to actually read everything you can. Gotta learn to pick and choose.