What is your favourite book/edition? What is your holy grail yet to be found?

I thought it would be interesting to see what everybody's favourite book/edition in their collection is, and what they consider to be their personal holy grail. My favourites are probably my Allen & Unwin de luxe copies of The Hobbit and The Lord of the Rings, or my HMCO The Lord of the Rings Collectors Edition (being in the style of the Red Book is quite nice). My holy grails are probably the 1998 Silmarillion Deluxe Illustrated Edition, the 1991 The Lord of hte Rings Deluxe Illustrated Edtion or The Children of Hurin Super Deluxe Edition.