This is one of those tutorials/tips that a fairly high percentage of you are going to say “uh I figured that out the first day I had my iPod Touch”. Well I had mine for about 2 months before I discovered this, completely by accident.
While you’re listening to music, but have another application open (like for example Safari) – if you double-click the bottom button, a series of controls (Previous Track, Play/Pause, Next Track, Volume and go to Music) will appear. You can use them and then return to Safari without ever having to exit it.
This trick even works when your iPod Touch is “locked”. Just double-click the bottom button, and you can control your currently playing music (though only Previous Track, Play/Pause, Next Track and Volume).