SetPower - time-based power management
SetPower is a utility that lets you choose different power management profiles for your computer based on the time of day. So, if you want your computer to stay on during the day, but sleep overnight, that's not something you can do with the built-in power management functionality in Windows. SetPower adds the ability to control which profile is in effect at a given time.
As the world becomes more environmentally conscious, the benefits of putting your computer to sleep when you might otherwise be inclined to leave it running are obvious. In fact, SetPower claims that you could save up to $10 per month simply by putting your computer to sleep overnight.
One of my pet peeves about software is that developers tend not to pay attention to whether the machine is running on battery power or not. This is particularly troublesome with software that runs jobs like indexing your hard drive, which can take a long time and keep your CPU running at a higher level then it otherwise would. That drains your battery when the software could very simply notice that the machine is on battery power, and wait until it is plugged in again. SetPower pays attention to the battery state, and can alter the machine's power management behavior depending on whether it is plugged in or not.
SetPower is free for home use, and an enterprise license is available at a reasonable $5 per machine.