A few books which really pulled my into fantasy that haven't been mentioned yet (or only glancingly) include the Dragonriders of Pern novels, The Dark is Rising series, The Giver, The Phantom Tollbooth and Heir Apparent.
I specifically remember Ender's Game and Dune as being SciFi revelations.
I also loved L'Engle's Time Quartet (Wrinkle in Time and its sequels). And, of course, I was too 11 when Harry Potter received his letter.