Some of these little LED keychain lights are actually very good and are virtually disposable items at $0.45 each.
http://www.dealextreme.com/details.dx/sku.1100They are very useful items to attach to tent zippers, pocket and bag zippers etc and forgotten about.
+1. I bought ten for $4.50 with free shipping. The first day I had 'em I left one in my pants pocket and accidentally ran it thru the washing machine, but it still worked!
![grin grin](/images/graemlins/default/grin.gif)
All ten worked fine and they're surprisingly bright. You may not want to trust your life to a 45 cent light but they're great for general use. I keep one on my keyring and a couple on various zipper pulls. So far none have failed.