There are a number of ways to get in a good workout in a short amount of time.  One way is to mix it up with a different set scheme.  Lets look at one right now.  The superset is a great time efficient way of cranking up intensity and shortening workout time aswell.  Supersets are a way to do fast workouts because you are perfoming two exercises back to back with no reak what so ever inbetween them.  So you could quite possibly cut your workout time in half if you put your mind to it.  It is also a great way to get through a training rut.