Since many years, I have this thing for folding papers into odd shapes;
I do origami.
It means, literally, "to fold paper". There are benefits to this, among them:
A note on the paper used: I have done origami using many kinds of papers, from coloured magazines (not sso good) to special origami paper from Japan. Mostly I use scrap paper from the printers at work, and lately I have used stickynotes. The glue strip offers both challenges and opportunities, especially in modular origami.
Below are some of the models I have folded through the years. Here I will only show models that I have successfully completed myself, which I liked, and I have created diagrams for.
The Simple Cube
Perhaps the simplest modular model, requiring no more than six pieces to complete, and it is also very easy to assemble. It is actually possible to make it even simpler by using paper with a 2x1 proportion rather than the 1x1 I have used.
Folding instructions are here.
This modular model takes 30 pieces to complete. The module itself is very simple to fold and it is also easy to assemble. I am not entirly sure that it will hold together strongly unless glued; I folded it from sticky notices and made use of the glue strip to keep it together.
Four-petaled flower assembly
Another modular model, but this uses only 24 square papers. The unit itself is not as simple as for Silvana's Star above, but not much harder. Three units form a kind of basket. They are locked together in a very robust way. Then, eight baskets are arranged to form the assembly. Here flaps and pockets on the outside of the basket is used. While it is possible to get it together without, I recommend some glue here or it will fall apart very easily.
The PDF with folding instructions is available here.