Exercise. Seriously, it keeps you healthy, gives time to think (away from a computer) and keeps your mind fresh.
A daily 5 minute half-brisk walk gives a disproportionate share of the benefits.
Running if for people to cheap to buy a bike:)
The advantage of cycling is that you get tired/bored when you are 30 miles away from your house. When I run, I get bored after a block, and can just walk home :)
Have you ever run in a natural park or a mountain?
It's been a great way to meet new people too.