I really think "A Wizard of Earthsea” is underrated. It really was one of the first examples of fantasy that was set in a society not based on Western ones.
My personal favorite is _The Tombs of Atuan_ - it introduces a new character, creates an entire world around her, then pulls all the assumptions beneath the world apart.
I second this. I think it was my first encounter with a genre book that totally "subverted" everything I had learned fantasy narratives should be.
I liked "Always Coming Home". And "The Lathe of Heaven" made a big impression when I was a kid.
I'd second The Dispossessed.
Through childhood association, my favourite is the first three Earthsea books, but probably her greatest writing is in her post-apocalyptic semi-utopia Always Coming Home, and maybe her most moving writing is in the 'story suite' Five Ways to Forgiveness (originally Four Ways...) on societies dealing with racism and slavery. Needless to say, her short stories are marvellous too.
The Lathe of Heaven [1]. My best example of a book written by one author in the /style/ of another author (in this case, her friend Philip K Dick).