Another easy method I found to get some exercise is in my office, at work in the afternoon.
A few years ago, I bought an exercise mat from Walmart that had a "15 Minute Full Body Workout" shown on it, with diagrams. So, I finally decided to give it a try. I also have a set of dumbells in my office, 20 pounds each, so I can do some weights as well.
I found it only takes 10-15 minutes to stop what I'm doing, close the door, and perform the stretching, body workout, and weights, and then get back to work. I was doing this almost every day, until I started doing stronger workouts in the gym, now I just do the mini-workouts when I feel like I need an extra boost.