Even if you are sitting there thinking that there is no way that you can fit 30 minutes of exercise into your day it is so much easier than you think because it does not have to happen all at once.
Walk your dogs in the morning for 10 minutes
Walk at one of your work breaks
Walk your dogs in the evening for 10 minutes
You can walk on the treadmill/elipitcal/stationary bike for 15 minutes
Walk 15 minutes at your lunch break
20 minutes on the eliptical
and only take stairs and park your car far away from the store that you are going to
The point is while the many exercise classes and videos are wonderful and great for you, the best exercise is the one you actually do!