Here’s a simple project that turns a 9V battery into a fully functional LED lamp. You’ll need one new 9V battery, one gutted 9 volt battery, three high intensity LED’s (white, 25.000 mcd – 3,8 volt and 20 mA – 35 degrees), and one magnet. One drawback:

The benefit of this is that you don’t have any losses in a resistor and the battery will end up lasting longer – but the LED’s will not operate on 100%.

[Grynx via MAKE]