My current favorite flashlight

The brightest single AA battery flashlight I have found that is really inexpensive is called Ultrafire C3 and can be found on Dealextreme.com. It uses a high output Cree LED and has a circuit that brings the voltage of the single battery up to operating voltage. The flashlight is small and packs a wallop. It's really bright.

The battery life is not very long but the thing is small enough to carry for quick use whenever you need it. It runs about $10.

For about twice the money you can get the Ultrafire Q3 6 mode which has the ability to change the brightness and thereby increase the battery life. There are three intensities and three flashing modes: quick strobe, slower double strobe and an SOS mode which just seems silly.

I have one strapped to my bike helmet in the slower flash mode and it lights up street signs for about 3 blocks.