Steppenwolf is a must read. I imagine many people on these forums have enough Haller in them to appreciate it.
True! Siddhartha and Damien are also inspirational.
For Carl Jung, Man and His Symbols.
From Aldous Huxley, The Perennial Philosophy and Brave New World.
From Ferdinand Celine, Journey to the End of the Night is essential!
From T.S. Eliot, The Wasteland and The Hollow Men.
From Houllebecq, Atomized and The Possibility of an Island.
From Tom Wolfe, Hooking Up, Bonfire of the Vanities, A Man in Full and The Electric Kool-Aid Acid Test.
But these are just background... to understanding what people are talking about here... it's easier and more fun than the philosophy reading for many.