The real trick is finding an exercise that burns calories, but does not provide a negative impact effect on your joints. I happen to like the Nordic Track cross country ski machine. It is a solid workout, and it is quiet enough that you could watch the evening news (30 minutes) while getting in a workout. One rather large problem is that a lot of people have trouble with the athletic coordination that is required with this machine. An excellent device that accomplishes the same benefits, but is much easier to learn how to use properly is an elliptical machine. A good machine will cost $500 to $1,000 but if it is acctually used, not just stuck in a corner, it will actually result in some serious weight loss.
chan