1.) http://idunno.de/weirdthingy.jpg

A quick weirdo-3D-puzzle. This was made from one piece of paper using only a few cuts with scissors. How?

2.) http://www.sciam.com/media/illusions/4.gif

3.) Not a puzzle, but strange anyway - Robert E. Neale's 2-way-tube:
http://www.counton.org/explorer/origami/2waytube.html

4.) http://www.idunno.de/strange.jpg

I'll just keep adding stuff as I find it.