The Left Hand of Darkness - Ursula LeGuin

All-around brilliant. Interesting setting; good, developed characters (though not many); and ever third sentence is so good you want to read it aloud two or three times. And all the sociology and political stuff seems enduringly relevant. "A man who doesn't despise a bad government is a fool, and if there was such a thing on earth as a good government it would be a joy to serve it." It's (along with playing Final Fantasy XIII) made me keen to write some big fantasy or sci-fi story.