I perform a circuit training workout that allows me to build muscle and shed fat at the same time. All of the lifts work 2 muscle groups at once so I am getting the maximum possible workout in the time that I have.
My routine works like this. There is 10 exercises. I do each one as many times as I can for 60 seconds. Then I rest for 60 seconds and do the next exercise for another minute. Once I have done all 10 I start again at the beginning and go through 3 circuits total.
The benefit of this workout is that it works you heart and your muscles at the same time. And believe me, it really works. By the end I am usually drenched in sweat and completely exhausted. But I am sticking with it because I am seeing results. In 2 months I have lost 25 pounds and developed the kind of lean muscular body that I didn't even have when I was 19.