Turn off your PC automatically while you are at bed, with Delayed Shutdown

Delayed Shutdown is a free tool that allows you to fall asleep when you are just listening to your favorite music or viewing evening television shows on your computer. Specify in what time your computer should turn off and just fall asleep while an evening show, your favorite movie or music is playing.

The minimum and maximum intervals are 5 minutes and 24 hours respectively. To cancel turning off the computer you can either close the program or click the Stop button.

If you use Winamp, you can also check the Winamp auto shutdown plugin.