The New York Times has posted their Tolkien Archives, including book reviews from back to 1938 and some audio snippets of the author reading each of the books. Included is a gallery of book covers over the years, including this map of middle earth from inside one of the jackets.
There are tons of fan sites out there, both official and not-so-official. The Land of Shadow isn't an official site but it's a pretty cool looking creation all the same. Maybe I'm biased because they have this slick, interactive map room.