The Most Dangerous Superstition, by Larken Rose. Accept no substitutes, this is The Bomb.
Atlas Shrugged is the book that woke me up (almost 50 years ago), but it's not my first recommendation any more. I've read more than half of the books I've seen mentioned in this thread, and many more libertarian classics. Rose's book tops them all for clear, irrefutable logic, without being in the least boring.
Another good choice: Why Government Doesn't Work, by Harry Browne. It has the advantage of being free, online.
If you prefer a novel, check out this thread.
Recommended reading: The Most Dangerous Superstition by Larken Rose
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