Music is very helpful to me when I'm tense. I think it's because there is such a powerful mind-body connection. Music forces my body into a new rhythm, literally, and my mind cannot help but follow along. Today, with iPods, cell phones, and streaming music on the computer, music is easily available to most of us.
Walking and swimming help me with tension, too, I think for similar reasons, making my body do something that forces it out of the physical manifestations of tension, also turning off the tension in my mind.
The ideal tension-buster is walking with music. (It's very difficult to swim with an iPod.) By the time I'm finished with a few miles, I am completely relaxed and ready to confront whatever created the tension in the first place.