GPS devices allow you to track your workout and figure out how long you went, what pace, how far, elevation change, etc.  These logs can then be uploaded online, evaluated to see how good you did, and compared with previous workouts.

There are tons of different options for hardware and software.  iPhone  users love to use the Nike+ sensor.  Android phone users enjoy software such as Buddy Runner or Cardio Trainer.  Then there are lots of GPS specific devices such as the Garmin Forerunner 305.

In addition to all of the above devices you have the Nintendo Wii.  The Wii fit game will let you get your workout in while having fun.  It will also keep track of your weight and whether you’re losing or gaining.  Other games like the Active Life Outdoor Challenge also try to help you to get that workout in.

With all of the great options available there is no excuse for not getting in a good workout.  Now if we can just get these devices to hide the donuts…