We've got a bookcase with 50% doored cells and 50% open cells. And I admit that we keep the 'better' books in the open cells. But that's as much for us and our own smuggery as it is for visitors.
In open shelves we've got:
A bunch of Iain Banks, Magnus Mills, Vonnegut, JB Ballard, Louise Welsh, and Pynchon (basically slightly dark, often satirical).
A bunch of modern classics, Steinbeck, Bukowski, Paul Auster, Hesse, Poe.
Some layman science books: largely entry level Quantum Physics (genuine interest).
Some poetry, plays and philosophy, fair bit of Nietzsche, ee cummings, Pinter, Rimbaud, Camus - largely relating to DH's degree, though he still reads them if he's feeling fancy.
And then kids' books, reams and reams of kids' books.