My top 10 are:
1. The Gutenberg Bible, 1st 1456 printing
2. THE NECRONOMICON, signed by Abdul Alhazred in his own blood moments before he was ripped to pieces by Cthulhu
3. DR. NO, Jonathan Cape 1958, 1st/1st in MINT condition
4. The galley proof of The Kama Sutra, circa 300 BCE with the unexpurgated illustrations
5. The Book of Life, flat signed by God
6. The 10 volume set of Paradise Lost by John Milton, 1667, with the free bookmark
7. The Egyptian BOOK OF THE DEAD in the original hieroglyphs, with the missing magic spell and the drawing of the pyramid on page 666 by the author
8. THE MODERN PROMETHEUS, 1818, one of two copies as written by Mary Shelley and rumored to be lost in a fire caused by a rather large monstrous creature with a daisy in his lapel
9. OLIVER TWIST, 1838 limited edition with the alternate 'twist' ending, as subsequently presented on the missing tape from The Twilight Zone TV series
10. The first issue ever of TV GUIDE Magazine (well, it's not really a book, but who
wouldn't want it?)