One of the unexpected benefits of my How to make business card cubes page is that the people who link to it also link to similar cool stuff. In this case, the serendipitous find is The Fitful Flog, an origami blog by Philip Chapman-Bell.
He's got great geometric models, complete with diagrams and photo how-to's. It's a lot more complicated than business cards, but also much more beautiful.
And while we're on the topic, here are some more paper folding links: