Not exactly a light project, still something CPF members regularly ask for.
During my visit to Eurobike, I saw 3 products that enable the rider to charge a mobile phone, GPS, ... from energy that the dynamo delivers.

1) Busch & Mueller "E-WERK" (Germany)
Input is dynamo, output delivers 2.8 - 13.3 V, 0.1 - 1.5 A.
Voltage and current limits are user-adjustable, making the unit highly flexible (assuming the user understands that wrong settings can burn his iPod)
The unit can run in parallel with dynamo light systems but will reduce the light output.

2) Tout-Terrain "The Plug" (Germany)
A 5V USB power supply that fits into the steerer tube.

3) PedalPower+ (Australia)
- PP+ DC output hub dynamo 5V / 600mA
- PP+ AC Universal Cable (fits any regular dynamo, AC hub or bottle types), 5V / 600mA
- Various standard accessories that feed on USB power. Includes solar cell + rechargeable battery units.