I have three motivators for running:
1)A partner. Having someone else who runs with me makes it all the more important I keep my schedule and commitment, not just to myself, but to my partner. Plus, having someone running with me motivates me to maintain proper speed and go the distance.
2)Self motivation. I really want to look great, and running is helping me see results. I want to see more results, so I keep running.
3)Music. I purchased an MP3 player, it comes with an arm bandso it's comfortable to jog with, and it's flash memory based, so it doesn't skip. I load it up with songs that help motivate me to run.
A fourth possible motivator is one you are using right now: support from a community. A group of like minded people working to lower their bodyfat, increase their lean muscle, boost their health, the worldfitness community.