If you are just getting started, I would get the Leslie Sansone videos "Walk Away The Pounds." SHe has many different routines, types of walking workouts and different time limits. They are all pretty good. I must warn you though, if you stick with them, fairly soon, they will not be "enough" of a workout for you. They are great for those that are just getting off the couch, but I don't think they are going to do much for long-term fitness.
I recently started using a highly rated tape by Jillian Michael's--The 30 day Shred. Each workout is about 20 minutes. It is not boxing, or lift 10 times your weight or anything like that but it is definitely intense for about 17 of those 20 minutes. And that's what you need if you are only doing a short workout.
I did do something stupid though, last weekend and sprained my ankle doing the jumping jacks. So I am on the couch for awhile.