Atlas Shrugged. I'm not a Rand groupie but seeing some of the core ideas of what I always felt but never could quite articulate literally changed me as a person.
Neither of us were (or are) objectivists, but it's one of those books that poke your buttons. Either you agree[1], you disagree[2], or you think it's insipid[3]. :-)
[1] Yeah, screw those looters who aren't as smart as I am! I mean, he is!
[2] Jeez, I hope someone drops a rock on these anti-social bastards. And what a floozy!
[3] You needed 80 pages for that speech? Weren't you reading this book while you wrote it?
Along with this, I would insist on The Law, by Frederic Bastiat. Written in 1850, this book still wows me.