If you want a 1AAA LED light and don't want to pay for an Arc, you could also try the CMG Sonic, $9.50 at TTS:

http://www.texastacticalsupply.com (click on "LED lights").

Review: http://flashlightreviews2.home.att.net/reviews/cmg_sonic.htm

I have both and the CMG is not as nice as the Arc, but it's not bad.

Also, the CMG/Gerber Infinity Ultra (AA sized, too big for a keychain but fine for a pocket) is hard to beat.