Sites

Hexaflexagon Toolkit (Popularity: )
http://hexaflexagon.sourceforge.net
A free application that can generate a hexaflexagon template and folding instructions from six user selected images. Examples Source Code included.

Flexagon Re'flex'ions (Popularity: )
http://hometown.aol.com/verndrei/flex00.html
Several possibly new trihexaflexagon phenomena are presented. The wide spectrum of findings including explorations with magic squares, palindromes, and much more freshly fans the flexagon fun.

Flexagons (Popularity: )
http://www.mathematische-basteleien.de/flexagons.htm
Includes a definition of the word, instructions on how to make a Trihexaflexagon, how to flex it and information about it and another flexagon.

Flexagons (Popularity: )
http://www.dtek.chalmers.se/~d3enar/Flexagon/index.html
Contains an introduction and history of Flexagons and a tutorial in how to make a Hexa-hexa-flexagon.

Flexagons (Popularity: )
http://db.uwaterloo.ca/~eddemain/flexagons/Conrad-Hartline-1962/
1962 technical report which includes an introduction to the history of Flexagons.