There's a fabulous exhibition on at the Bodleian Library in Oxford right now, called Magical Books. I can't recommend it highly enough.
My favourite exhibits included pages from the Rawlinson Necromantic Manuscript (I kid you not); Alan Garner's beautifully handwritten manuscripts; Tolkein's handmade facsimile of the Book of Marzarbul ('they're coming!'); and a medieval book of divination, the Prognostics of King Socrates, which included a pair of interlocked leather cogs, called a volvelle, used to generate random numbers.
Oh, there's some J. K. Rowling 'abilia too, if such things float your boat. On till September, and well worth the trip to Oxford.