Mine is either The Demon-Haunted World or 1984. Both are so important. Everyone in the world should read these books. What's Yours?
My great grandparents grew up in the dust bowl (before they escaped to California) so I relate to that book alot. It reminds me of family.
Check out The Rum Diary, Fear and Loathing in Las Vegas, and Screwjack. --- My favourite of the 20th century would have to be 'Fear and Loathing in Las Vegas'