It appears that the Nintendo DS Lite was made for solar panels, as the Instructables author dark sponge has created a useful solar charger for the DS Lite. The top face has enough space for two 60x60mm solar cells side by side, each outputting 3V at 40mA.
By installing another 2 solar cells on the bottom of the DS. Each pair is wired in series, and the 2 pairs are wired together in parallel. This gives you a total of 6 volts at 80mA, perfect for charging a DS lite. To charge the DS, you simply open it out and leave it in the sun. The article was recently updated to use a charge protection circuit, so keep an eye out for the revised Instructable.