I agree with the endorsements of The Master and Margarita, Brautigan, Bukowski, Hemingway, Vonnegut and Doyle.
Choosing a favorite five is all but impossible. Imagine being dropped in the Chicago Art Institute and told, "Pick the best five artworks here." Still, I'll name some of my perennial favorites:
1) To Kill a Mockingbird. IMHO, no one needs to try to write the Great American Novel. It's already been done. How much do I love this book, you ask? Well, my daughter's name is Scout. (She has a more traditional first name as well, but Scout is one of the names on the birth certificate, and we've never called her anything else.)
2) The Fountainhead. Yes, Rand's work is lacking subtlety in the same way a jackhammer to the forehead lacks subtlety. No, she couldn't read philosophy. Yes, her own philosophy is riddled with flaws. But the novel still stands as one of the best paeans to individualism, excellence, and passion ever written.
3) Ecclesiastes. I'm not a religious guy, but some works are genuinely timeless. The gorgeous prose and universal observations in that work make it one of the best things written by anyone, ever.
4) Locke- Second Treatise on Civil Government. This is not a beach read, but the foundations of liberal democracy are all here.
5) Plato-Pheadras. Too much to cover in one paragraph. Just read.