Microsoft Research developed a small e-paper (E Ink) based display that harvests its entire energy using photo-voltaic cells on the back. Using low-energy bluetooth the device connects tot he network every 1-25 minutes (depends on the ambient lighting) to update the display.
The display itself seems very small (around 2-3 inch in size and is a very low resolution one). This is a very neat little gadget, although it's unlikely this will be turned into a real commercial product, at this stage it is just a research project.