Solely based off my personal experience but worth sharing, I think.
If you are like me and have a loud head with thoughts that rarely let you rest, I have found that only physical activity combined with either an element of fear, intensity, or deep concentration can stop the chatter. My top choices are a hard Aikido class preferably with jiu-waza to keep the body and mind constantly engaged or sparring practice since you need you continually react, block, and get out of the way. Body-boarding on overhead waves will work too but only if they are rapidly moving. The constant duck-diving and then lining up for waves, and then riding waves is terrifying, tiring, and thrilling and unless you catch a super long ride (at Over the Reefs or Walls) you likely won't have time to think at all. Last, is running, but only if you have an ipod with an awesome playlist. For me running is still challenging enough that I have to focus and really let the music help me escape.
If you don't have time for a full-on activity, try riding your bike. I swear, being back on the bike has improved my mental health by about 5%. I also end up having about 40 extra minutes in the day that were previously taken up with walking to and from campus. For this week only I am vowing to not cut off any cars or run red lights. I'll still be racing up the hill, can't help it!
Fast-paced video games are also an escape.
I wish I could say that I use meditation or yoga to clear my head but those things don't work for me. Yoga does help my body feel amazing which then reflects on my body-image and gives me a sense of strength and balance but it does not allow me to clear my head. Meditation seems to lead to me fidgeting, falling asleep, or it gives my mind more of an opportunity to take me to places I don't want to visit. I realize with the latter that I probably have not taken it seriously enough...
I am a 100% believer in the mind-body connection when it comes to health and well-being. Though I may use exercise and physical activity to turn off my mind, I view it as letting my mind have a rest from worries, anxiety, and running thoughts and instead allowing it to focus on being intuned with the ocean (body-boarding, diving, swimming), an attacker (martial arts), or music (running).