Whilst this may not be pertinent to everyone, if you are a laptop user with Windows Vista installed, then you might like this.

BattCursor is a small utility that changes your mouse cursor to show you how much battery life you have left in your laptop.  Very simple idea, but it works rather well.  This utility does a bunch of other things as well, but the ability to constantly see the state of your battery is very appealling.  Take a look.