Cat's Cradle by Kurt Vonnegut - I really need to go back and reread this along with a few others of his masterpieces. Still, this book got me hooked and served as the foundation for this massive term paper I wrote back in school. I was tasked with reading at least 4 novels (with no direct series type ties) by a singular classic American novelist. We then had to examine the author's styles and themes to find underlying ties specific to their works. I think I wound up reading 6 of Vonnegut's books for this one. Slaughterhouse-Five was the real star, but I wouldn't have gotten there without Cat's Cradle.
Harry Potter and the Prisoner of Azkaban by J.K. Rowling - It's not my favorite of the series but this was the book that convinced me I had to read the stories and that the movies were simply not enough. Truth be told, the first two books and movies mirror each other pretty well. After Azkaban came out in theaters, a coworker who was reading first then watching insisted I read her copy so that I could experience everything I'd missed by just relying on the movies. She was soooooo right!!! I'm grateful for her doing this because Goblet of Fire was significantly better in book form compared to the shell of a movie that was produced. Don't get me wrong, the movie is entertaining, but it doesn't do that part of the storyline justice.
If I Ran the Circus by Dr. Seuss - This is one of my absolute favorites, but I think it's also because it's one that my dad would read to me and make up all kinds of funny voices and sounds to go with the story. I also always loved it because it challenged the creative mind to think about the possibilities beyond the commonplace and mundane things you'd expect in life. This one was my first of this kind but, Scrambled Eggs Super, McElligot's Pool, and If I Ran the Zoo also really made you contemplate exploration and discovery beyond the obvious.
