I made it using arduino fio.
Take a look at video and pictures.
http://arduino.cc/forum/index.php/topic,49986.0.html
The fio has a built-in max1555 li-po charger and you can plug your solar cells/panel directly to fio. Also you can transmit serial communication using the integrated xbee socket.
actually I don't know if I need a diode or no on my solar cells. I made a post about this and I'm hoping somebody help me:
http://arduino.cc/forum/index.php/topic,50338.0.html