They're a bit complicated and somewhat experimental, but these instructions for homemade organic LEDs are nothing short of thorough. Sure you can just buy OLEDs, but that's just not even half as fun as struggling to make them yourself.
These instructions were written up by the folks from the Materials Research Science and Engineering centre at the University of Wisconsin and could very well be the blueprint for my next weekend project. Anyone have any pointers though? [University of Wisconsin via Erik de Bruijn via Open Materials via Make via GooHack]