The power of junk! Here is something really cool to make out of a tape player/ or CD player and a LED. Any old LED will work, but it will be a lot brighter if you can find some 5mm white ones. Pretty much all LEDs will run happily (and forever) on the low current supplied by a tape/CD player motor.
What makes this project really cool is that the end result is not just a demonstration of free power generation, it's also quite practical. The LED is blinding bright... I always keep one handy in case of a thermonuclear exchange induced power outage.
Here's a video. It was kinda hard to take a video while spinning it...Oh, and I find it easier to spin it towards me (more leverage or something).