Update 11/05/2012. I now use LED flashlights that are rechargeable and much brighter that what I originally mentioned in this instructable (a 3 AAA LED light from Sams Club). Amazon is a great source
for these types of lights and batteries. There are plenty of resources for LED flashlights of all sizes, prices and brightnesses. Google is your friend. Most of these lights use a Lithium Ion battery that is commonly called an 18650 battery. LED technology has also come a long way, Cree and SSC have LED's that are capable of upwards of 900 lumen. If you want to go smaller and lighter there's also a battery called a 123 size. They're half as long as the 18650 batteries and allow for smaller lights
that are still amazingly bright.