Left Hand of Darkness is a great place to start, especially if you're the sort who likes the idea of, oh, our two main characters having to huddle for warmth in the middle of a blizzard while one of them in going through Ponn Farr and the other one is trying to teach them mindspeech. :D So is the Earthsea trilogy(= six short books), if you're the sort who likes YA fantasy. And Birthday of the World is a short-story collection that gives you a great sampler.

Really most of her stuff is good, but some of it is a lot denser than others.