Actually, I had. I now have planted in the back of my mind the festering thought, “You’ve read about this. You have a (very) vague idea what it was supposed to be about. You will not be able to rest until you have dug through your collection of Heinlein-related material and solved this mystery.”
Damn you, Weird Al 
I’d like to get a look at The Slayer’s Handbook * and the other works in the private collection of Rupert Giles on * Buffy the Vampire Slayer.
I’d also like to examine that map Bugs Bunny uses when he makes that wrong turn at Albuquerque.
The Book of the Dead is very real. It’s the Ancient Egyptian’s Guide to The Afterlife. All of the supplications, rituals, and routes the ka will need to know to advance to the good afterlife. I actually have a direct translation: Heiroglyphs on top, phonetic transliteration below, and English translation lowest. Line-by-line. It’s a huge book, and nearly unreadable because of the directness of the translation (‘odd grammar’ doesn’t begin to describe it).
My favorite fictional book is The Necronomicon, which is completely fictional. Since that’s been mentioned, what’s the name of that book from Beetlejuice the couple was issued/found in their attic upon death? I think it was like So You’re Dead. I want that.
I want the Black Dog games from the World of Darkness.
The Complete Art of Detection by Mr. Sherlock Holmes. Alledgedly completed during his retirement in Sussex, I assume it was written during Winter, when beekeeping was not a demanding pasttime. 
Also, the unpublished short stories & novels in Watson’s tin dispatch box.
Handbook for the Recently Deceased.
And from Eddie Izzard’s Dress to Kill, the Gospel of Saint Bastard.
The book I’d love to have isn’t from a movie, but from a band. The Helping Friendly Book, from Phish’s “Gamehendge” saga…It contains all of the knowledge in the universe. A great book to have, I’m sure, but it must be a bitch to carry it around…
Yes, but can reading it cause 3000 year-old corpses to get up and walk around?
The fictional book I really, really want is…
Women Who Find Doc Cathode Attractive
(Unabridged Edition)
or maybe
Insane, Jewish Women Willing To Marry Doc Cathode
Why stop at Mabel Syrup? I’d like that book that Dad has: the one that tells you everything about everything. It tells you about trees sneezing, and the like.
Another vote for the terrible Necronomicon of Alhazred.
And what about the monograph Professor Dyer wrote after Miskatonic’s Antarctic Expedition?
How about the one on the Family Guy episode where they think that Stewie has to be potty-trained? My memory on the exact name of the book is shaky and I don’t feel like watching the episode for the real name, but the guy at the bookstore suggests a title, and Peter says, “Oh, but we’re Catholic.” Then the bookstore owner says, “Oh, then you’d want 'You’re a Naughty Naughty Child and That’s Concentrated Evil Coming Out of You.”
Audiobottle
I’ve got a copy of The Invisible Book Of Invisibility around here somewhere…it was just here…I think…where’d I put that?
I also wouldn’t mind a copy of Bugs Bunny’s Magic Woids and Phrases .
“La da da di da di da Hocus Po-o-o-o-cus!”
Last night’s Six Feet Under reminded me of one.
I would love to read Charlotte, Light & Dark.
Curious George and the Ebola Virus
The Book of E-Ville and the Book of Gud (how do you make umlauts?)
I’d like the super-suit instruction manual Hinckley kept losing on TV’s The Greatest American Hero.
Of course, I’d need the suit, too.
YAY SLUGGY!!!
The actual title of the real Egyptian Book of the Dead is “The Book of Going Forth by Day.” I mention this only because I think it’s a really cool title.
My Name is Susan Snell in Steven King’s Carrie
Learning to Grow by Lily, in John Irving’s Hotel New hampshire
I can’t remember offhand, but it seems like all the characters wrote books in Irving’s The World According to Garp