For me the best motivator has been witnessing the success of a good friend's side project [1]. That, and I've also found that it's really important to commit to imperfection. It's better to have something small out there garnering feedback than it is to build something in a vacuum for months at a time.
Try taking a planned weekend to scrap together the absolute minimum features of your project that might be useful to another individual, and publish them. Commit to actually publishing by the end of the weekend so long as at least one other person might find usefulness in your work. Publish no matter how imperfect it is. My side project's [1] plan is a gazillion times bigger and more interactive than what's implemented today, but what finally got it out the door was the exercise I just described.
Try taking a planned weekend to scrap together the absolute minimum features of your project that might be useful to another individual, and publish them. Commit to actually publishing by the end of the weekend so long as at least one other person might find usefulness in your work. Publish no matter how imperfect it is. My side project's [1] plan is a gazillion times bigger and more interactive than what's implemented today, but what finally got it out the door was the exercise I just described.
[1]: http://corkboard.me [2]: https://threadcheck.me