This isn't a very creative idea, but I guess I'll share anyway:
Step outside - somewhere without people or technology. For me, it helps if it's sunny out, too.
I don't know what it is about being alone outside during a sunny day, but it helps me relax..
It's what helped me calm down today, too. I just stepped out of the house and sat on the porch in the sunlight, just watching the trees sway, watching little bugs crawl around in the dirt, listening to the goats baa in the distance, etc.
I would have loved to go on a walk, too.. but I knew I'd get lost, so I didn't leave the yard. haha.