Get a light with multiple levels. My favorite ones have an extremely bright beam when you need it, and a low low that will give you around 10 hours of battery life on a single AA. My favorite light lately is the DX.1 from dealextreme.com. Sapphire lens, HA III, double o-rings on both ends, etc. I have had mine for a few weeks and love it. It has some ridiculous amount of levels (17, I think), but the first two when you turn it on are the most useful. The first is a blinding high, and a soft press will switch modes to a low low. It is currently $45 from them. There are a few other lights on the market now that are very similar, but this one seems to be the easiest to get with the most consistent quality. Plus, you can get a pig shaped LED keychain for $1 from DX. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

Fenix lights are OK, but I think there are better ones out there (disclaimer: I like flashlights way more than the average person). They do have about the most efficient circuits of anyone though.