[RTigger]

I like to set external-facing deadlines. I'll do things like tell my department I'm going to do a presentation on technology X in two weeks, and then start learning about it. If I don't get it done, I have to tell 20 other developers why I have to cancel the meeting they've all accepted.

This is part of the motivation of team and peer-accountability in some of the agile methods like Scrum / XP / Pair Programming. If you feel personally responsible to someone else, you're likely to follow through. A good way to do this with personal projects is to find a partner - I work with a designer on a lot of my personal projects, and telling him that I'm going to get X done helps, as well as seeing the time and progress he's invested in the project.