One of the best ways to get the most out of your workout (and to beat boredom and prevent over-use injuries) is by cross training. This means you use a variety of different methods to get your heart rate up in one session.
Warm-up -- 5 minutes
Bike to your local park -- 15 minutes
Run -- 20 minutes
Bike back home -- 15 minutes
Cool-down -- 5 minutes
This way, 60 minutes have gone by before you know it. Don't own a bike or have a park that's within biking distance? You can achieve the same idea at the gym by using the stationary bike and the treadmill.