Ride a bike (I'm being serious)
Article - "When I was anxious and depressed, cycling put me on the road to happiness"
Surprisingly, I've already tried that. Not as a way to relieve anxiety, but I've tried it.
Well, I hate it. All the bicycle paths in my city always have a lot of people on them, and I end up getting really stressed trying to not bump into anyone or anything.
I actually played tennis for a period of time and it helped me a bit to relieve stress, but I moved and there are no tennis courts around here. And now with college, I don't really have much spare time.