My banned book pick is Farenheit 451, by Ray Bradbury (1953).  While there are so many amazing books to choose from (Lord of the Rings, James and the Giant Peach, Cat's Cradle, etc.) I couldn't resist choosing Bradbury's classic novel.  Set in a future in which free thought and expression are discouraged and books are illegal, I can't help but point out the bizarre irony of banning a book about the evils of censorship and book banning

On the surface, Farenheit 451 was banned because the author used "hell" and "damn" in the text, but it seems pretty clear concerns about the book's message about ran deeper.  The book was published in the era of McCarthyism, yet it encouraged the average person to oppose government's suppression of freedom of speech and expression.  Sadly, over 50 years later, it's still an important (and potentially threatening) message. 

I feel lucky to have read Farenheit 451 (twice so far), and to live in a time and place where I can do so openly, and in public.  If we heed Bradbury's warning, and take up his message, I hope to not have to hide my copy in the walls of my air vent any time soon.

“A book is a loaded gun in the house next door...Who knows who might be the target of the well-read man?”
Ray Bradbury, Fahrenheit 451