Well after saying how you can get books owned by Tolkien or his family, it's come true. davem was after a set of Gibbons' The History of the Decline and Fall of the Roman Empire after enjoying the easily available abridged version; he was looking at a full set of paperbacks in Blackwell's in Oxford but didn't buy them. We since found out that a dealer had a set which came from Michael Tolkien's library, and he's bought them. They are a lovely set of books, and they will not just be put on a shelf but will be read and enjoyed. They were actually bought by Tolkien himself and given as a birthday gift to his son - they have bookplates in each volume.
I find it a bit weird to hold books that had been bought by Tolkien, books he'd chosen and handled. Looking at the bookplates it struck me how Tolkien was not just a mythic name, a personality to be dissected, he was as real a person as I am. He'd also leafed through the very same pages...Kind of a spooky sensation...