I've been using a piece of software called Pzizz for the last couple of weeks, and I really like it. I'm using the OS X version, but there is a Windows version as well.
Basically it generates audio files that you can put on your MP3 player for "power napping"enjoyment. You specify the length of the file and a few other options and then it mixes the file from some large set of audio clips. It's all a bit New-Agey sounding, but it seems to work. Some of it is hypnosis techniques - there's a voice that leads you through what are centering and meditation exercises, some of it is just quiet, and supposedly they are doing some odd stuff with sounds to induce particular brain waves and promote relaxation.
Like I say it all sounds goofy, but it does work - basically you end up taking a 20 minute nap/meditation and come back feeling quite refreshed.
The software lets you try it three times before paying anything, and I recommend it. The web site seems a bit heavy on the snake oil, but ignore that and just it a whirl.
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