I'm fortunate to work for a local police department that has an in-house gym. I started walking in the mornings a couple of months ago, working my way up to 3.2 miles 6 days a week. This week I decided to start going back to the gym a couple of times a day and doing 5 minutes at a time on one of the elliptical machines. 5 minutes doesn't sound like much, but when you were a couch potato like I was, that extra 10 minutes a day makes all the difference in my calorie burned department!
The best part about it is that I'm not gone from my desk for very long and I don't get totally sweaty and nasty like I do in the mornings from my walk.