In my early twenties, I learned to meditate and at one point in time was spending two hours a day at it. Haven't done it for years, but now I find that it can de-stress me within a few minutes. I can go from a state of fairly high anxiety, usually over some about-to-happen social event, through feeling my whole body relax to feeling almost surreally calm. It doesn't stay that good when I move on, but there is certainly a lingering lessening of the anxiety. I'm thinking it would be a good thing to do regularly again, not just as an emergency measure.

Walking outside always makes me feel better.