Exercise does help, when I'm really stressed I go out on a walk/jog for a mile or two no matter how late (2:00am is my record). Whenever I regularly go to a gym weights do a better job than walking.

Other than that, make sure you don't let your work flow into the weekends. Make sure it is known among your clients that you don't work weekends and anyone who expects you to will be disappointed. Do something during that weekend, go to a bar with some friends or something. Just sitting around all weekend is just as bad as working it.