Motivation comes in many forms, and can be quite different for all of us. Are you motivated by a reward system, or would you rather tick things off a list. Perhaps social contact helps more, so finding a buddy would be the best way to go about things.
What has worked for you in the past?
I know that my motivation wanes each time I finish a race goal. The training plan is over, and I need to set something up fast so I have something to follow. One of my methods is the list (which the training plan works well - I can cross each workout off as I work towards my goal).
I am also motivated by streaks. How many days in a row can I get in five veggies/fruits?
And my teams really motivate me. Sometimes I just need to read about someone else struggling with arthritis (or whatever), and they went out for a walk anyway - and this helps me to go out too.
Motivation is a large topic, with many different faces to it. SparkPeople has a whole resource section dedicated to it. www.sparkpeople.com/resource/motivation.as
Hope this helps. Keep the discussion going - it will help you to find ideas for yourself.