Apple has applied for a patent that may lead to iPods and iPhones containing solar cells in order to charge the players. The interesting part about the patent, dated April 24, 2008 and titled "Solar cells on portable devices", is that the solar cells actually sit beneath the screen itself. This would allow a full screen device (iPhone, for example) to receive light from the direction the screen is pointing, allowing for maximum usability while still siphoning off a charge.
It will be interesting to see if this makes it into production any time soon, but at least we are seeing a peak at the future of portable devices.
Aloha from the Beach