Literature and poetry mostly. I like folks like Joyce, Fitzgerald, Hemingway, Saroyan, Jean Genet, W. Burroughs, Irvine Welsh. I like how it seems to make some sense of the world.
And I like poetry, like that of Baudelaire, Fr. Villon, Kipling's stuff.

I also think taking time to read biographies of people you admire is helpful to everyone.

Motivation and self-development books can also be an asset, provided you manage to edit out some of the BS that many of these type of books contain.