Lots of people use their computer for almost anything. So why not use it as an alarm clock, waking you up from your dreams? And what about reminding you to go for an appointment right away before it's too late while being engrossed in something else on a computer?
There are lots of alarm clocks on the internet, but most of them don't wake your computer from standby or hibernation. Why leave your computer running all night just for one important task: to wake you up?!
These are freeware programs which might be useful and interesting to you if you don't like that waste of energy either.
Discussion

You could use it as an alarm clock by starting up internet radio or m3u-playlists. It works nicely in combination with another one of the developer's free tools, called Toff, which puts your system to sleep.

The program has a customizable snooze as well as a standard activated, volume-level control.
Not all soundcards support this volume control though, so you should test if your card supports it or you have to turn this option off.
Simple Alarm Clock, a really simple version from the same developer that just does what it's supposed to: Waking from standby/hibernation and running the file you want.

You can set as many alarms as you need, choose the sound for each alarm, label it and indicate in the text field the activities you need to do at the times you set.