Solar Powered Mac Keyboard by Logitech. This keyboard addresses my number one complaint about wireless anything (which is why my keyboard and mouse are both wired), which is, the need to swap out the batteries.
Behold, the Wireless Solar Keyboard K750 for Mac:
According to the company, even standard indoor lighting is enough to charge the keyboard, and with a full charge, the K750 can operate for three months in total darkness. Which means that in real-world use, you should never have to worry about running out of juice.
Sounds very impressive. I just might try one of these out.