When looking for interesting Leaflet fold research I stumbled upon a page that explains all the basic folds that people should know called '9 Diferent Leaflet Folds'. Most of their folds can be seen in the diagram below.
There are always ways to improve upon the simple folds as done below with the concertina fold with an angle. It makes the design more engaging as you can see more content when it is closed.
Keith Lowe
Kieth Lowe designed this beautiful leaflet that has incorporated its folds to give the illustration on the front a 3 dimensional look. The only downside to this style is it makes for a more difficult reading experience when the design has opened fully.
