People exercise for different reasons, and everyone should be exercising regularly. That's easier said than done. You definitely have to have a few tricks up your sleeve to help you stay motivated. Here's one of mine.
I bought an iPod Nano ($150) and Nike + iPod Sports Kit [0] ($30) and I use it every time I go for a run or walk. Basically you plug the receiver into your Nano, and attach the sensor to your left shoe. Nike makes special Nike + sneakers (of course), and the sensor fits snugly in the shoe under the foot bed. I like to wear whatever brand of sneaker I want, so I just use a RunAway [0] ($7.99) - it's a waterproof capsule that holds your sensor and attaches to your laces.

Want to know how it works? Then
When you go for a run or walk, the sensor on your shoe monitors your time, speed, distance, and how many calories you've burned (just wish it had a heart rate monitor too). If you hit the center button on your Nano, you'll hear a voice tell you all that info (very cool). Then when you get home, just plug your Nano into your computer and all your data automatically gets sent to NikePlus.com [1]. It keeps track of all your runs, so you can track your progress.

You can even set goals for yourself, like run 12 times in 4 weeks, or run 20 miles in 4 weeks. I set a goal to burn 1800 calories in 4 weeks and when I reached my goal I got a "Congratulations," and a little award in my virtual trophy case. It's kind of like those gold stars [1] I put on my calendar - a little silly maybe, but very motivating.

The bottom line is you need to find what motivates you. Tracking my progress online really gets me on a regular exercise schedule, and because I can see my stats in stone, it motivates me to keep pushing my personal limits.