I will browse the Internet (Youtube, Facebook, and of course EF ), take small coffee breaks, and generally try to find some time to be alone with my own thoughts.
I like to listen to a few songs on my iPod or take a little walk (if it's between midnight and 5 am, otherwise I relax on the porch or walk around in the yard).
Though if I'm really stressed it usually takes me a while to cool down so neither of those things help then. That's why I like to try and keep my stress levels in check so I don't get too frustrated.