What is the best health/exercise program to do in the workplace?

A gym or walk. I have noticed that a lot of big corporations have now added a gym in the building. Employees can now work out before or after work or during lunch. Employers have noticed more productivity by those employees who work out. There is more blood flow to the brain so they are sharper on the job. If you work for a smalller company, a walk around the parking lot may help. Also, take the stairs!
Move. Unless your workplace has an exercise facility, this can be difficult. Get up and walk as much as possible, take the stairs whenever given the chance. Take some time at lunch to walk get in a quick trip to the gym.