Honestly, Crossfit has been the best boon for me as far as staying in shape and having a horrid schedule is concerned. I work 40 to 50 hours a week, but I also go to school fulltime. (2nd time through college mind you). Between that, and my time with my girlfriend, I don't have a lot of time.
Crossfit can either be done in groups, or solo. It is quick, intense, and burns far more calories than you'd burn with hours of time on a tredmill or some other crap. Many of the exercises can be done anywhere, even in an office, and dont' require you to go to some big Globo gym.
Just check out www.crossfit.com, and you'll see the daily workouts, free videos describing various movements, and all that jazz. Long story short, it's helped me get back in shape, and still have my insane and stupid schedule. As other said, eating right is key as well. I bring almonds with me to work, and try to eat along the lines of the Zone diet.