BOOKS are often forgotten in the digital revolution.

Yet the demand remains and many out-of-print books have become collectors’ items and very valuable.

What are the most sought-after out-of-print books? Bookfinder.com has released its latest list. Pop singer Madonna’s revered coffee table book Sex, published by Warner Books in 1992, tops the list as it has done since 2011.

The book, which was packaged in aluminium and is spiral bound and enclosed in a Mylar sheet, was an instant commercial success, selling over 150,000 copies on its first day of release and topping the New York Times’ Best Seller list.

It was released — in five continents and in five languages — the day after Madonna’s Erotica album in a blaze of controversy with the Vatican calling for Catholics to boycott it and Japan banned it from sale shortly after its release.

“I don’t think sex is bad. I don’t think nudity is bad. I don’t think that being in touch with your sexuality and being able to talk about it is bad. I think the problem is that everyone is so uptight about it and have turned it into a bad thing when it’s not. If people could speak freely, we would have more people practising safe sex, we wouldn’t have people being sexually abused,” said Madonna, who is playing concerts in Australia in March, said in response to the outcry towards her book.

Stephen King has four titles in Bookfinder.com’s top 100, including the second most sought-after book Rage, which was published in 1977 under the pseudonym Richard Bachman.

Rage was taken out of print in 1997 after Michael Carneal shot eight fellow students at a prayer meeting in West Paducah, Kentucky. He had a copy of the book within a Richard Bachman omnibus in his locker. The book had also been linked to school shootings in the US in 1988, 1989 and 1996.

King’s short story My Pretty Pony, which was a limited print edition of 250 in 1989, is the third most sought-after book out-of-print. My Pretty Pony was the sixth publication in the Whitney Museum of American Art artist and writer series and was originally published as an oversized slip-cased book with stainless steel faced boards and a digital clock inset into the front cover.

A trade edition of 15,000 was later published by Alfred A Knopf and was later included in King’s collection Nightmares & Dreamscapes.

Abebooks.com reported that The Afronauts, a photography book by Cristina de Middel, makes the top 20 most sought-after books out-of-print for the first time.

Self-published in 2012, The Afronauts reimagines the true story of a bizarre Zambian space program in 1964.

After Zambia’s independence in 1964, Edward Makuka Nkoloso, the founder and only member of Zambia’s National Academy of Science, Space Research and Philosophy, initiated a mission to send the first African astronauts into space, and more specifically — wait for it — to Mars, Telegraph UK reported.

Nkoloso set up a secret HQ near Lusaka, where he and his team studied the stars through telescopes and underwent gravity training by rolling down hills in oil drums. According to a contemporary newspaper report, Nkoloso claimed that Zambia’s first rocket would contain ‘specially trained spacegirl Matha Mwamba, two cats (also specially trained) and a missionary’. The project never eventuated and De Middel’s images show Zambians dressing up in Buck Rogers-style space outfits made by her grandmother.

Copies are now selling for more than $1,000.

The BookFinder Top 20 most sought after books out-of-print

1. Sex by Madonna

2. Rage by Richard Bachmann/Stephen King

3. My Pretty Pony by Stephen King

4. The Harvard Classics (51 volumes) edited by Charles W. Eliot

5. On the Nature and Existence of God by Richard M. Gale

6. Promise Me Tomorrow by Nora Roberts

7. The Jerusalem Bible by Salvador Dali

8. A Treasury of Great Recipes by Vincent & Mary Price

9. Mandingo by Kyle Onstott

10. The Centurions by Jean Larteguy

11. On the Psychologyof Military Incompetence by Norman F. Dixon

12. Labyrinth by A C H Smith

13. 365 Bedtime Stories by Nan Gilbert

14. The Road We are Travelling, 1914-1942: Guide lines to America’s Future by Stuart Chase

15. The Afronauts by Cristina de Middel

16. The Body by Stephen King

17. Mastering Atmosphere & Mood in Watercolor by Joseph Zbukvic

18. The Angelique Series by Anne Golon

19. Murmurs of Earth by Carl Sagan

20. Beyond the Plough by Janet Woods

For top 100 visit bookfinder.com