Wizard of Earthsea if you want a good fantasy story with good morals. And then from there its sequels are also great.

The Dispossessed if you want an exploration of what a fully anarchist society might be like, and how it would related to a capitalist one. I hear the other stuff from that loosely related collection of books (the Hainish cycle) are also quite good.

Haven't read any of her nonfiction.