I like anything by Teresa Tapp.

20 or 15 minute workouts. No equipment required, and can be done in a small footprint like a bedroom. The trainer used to work with models who have no time or space and travel a lot and need to keep the inches small as possible.

Very fun and they really get your heart up and your muscles sore.

Check out the Try before You Buy , and the physiques of the people who do it. Very nice.