Jurassic Park by Michael Crichton. One of my favorite summer reads; I couldn't put it down. 99.9% different from the movie and that is OKAY.
The book...much better than the movies.
The Lost World- It's hard to separate the movie with the book in my mind since I read the book so long ago but I love all the Jurassic Park books. I've always been fascinated with dinosaurs and I love jumping out of my seat when dinos jump out at you. The big cage scene with the pterydactyls in the third movie was actually in this book.