4. Cube books
Inside Rubik's Cube and Beyond, by Christoph Bandelow,
Birkhäuser Boston, 1982.
This is the best cube book ever written.
Besides the clever title, it also has a section on mathematical theory,
a solution understandable to the average person, amusing cartoons,
an exceptional collection of pretty patterns and maneuvers,
and a flowchart for a cube-solving program.
The German edition of the book,
Einführung in die Cubologie is earlier, and not quite
as complete as the English edition, but I've heard it's also very good.
Notes on Rubik's Magic Cube, by David Singmaster, Enslow, 1981.
The first book to appear about the cube and the most influential.
This book popularized Singmaster's "FLUBRD" notation and other
conventions which have become standard.
It's not as polished as Bandelow's book, but it appeared much earlier.
Appendices were added as new information was discovered.
You can see cube history unfold before your eyes as you read them.
It's still a classic.
Winning Ways (volume 2),
by Elwyn Berlekamp, John Conway and Richard Guy, Academic Press, 1982.
It only has a brief section on Rubik's Cube, but it's quite worthwhile.
Many other games are discussed, including Conway's Game of Life.
Handbook of Cubik Math, by Alexander Frey, Jr. and
David Singmaster, Enslow, 1982.
This book supplements Singmaster's Notes on Rubik's Magic Cube,
by taking a closer look at the group theory behind the cube.
Rubik's Cubic Compendium, by Ernő Rubik, Tamas Varga,
Gerzson Keri, Gyorgy Marx and Tamas Vekerdy, Oxford University Press, 1987.
English translation of A Buvös Kocka,
with an afterword by David Singmaster.
Cubic Circular, by David Singmaster.
A short-lived periodical in 8 issues.
They are now
online at Jaap's page,
but you are encouraged to purchase print versions from David Singmaster.