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 ($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 ($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. 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 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.