The new iPhone app EpicWin attempts to solve that problem. It’s a simple to-do list application that encourages you to use it with a unique RPG-style angle. You create a character and level up by completing the tasks you assign yourself. You can mark a to-do item as being worth a certain number of experience points, which go to the relevant skill you designate.
For example: I need to write a blog post today, so I add the task “Write blog post on Webmaster-Source” to EpicWin. I assign it 100xp and list it as a feat of Intellect (as opposed to a feat of Strength or something similar). Once I finish the task and check it off, my character is awarded the experience.
I downloaded the app as soon as it went live in the iTunes store last week, having been anticipating its release for a couple of months now. I think it will (hopefully) be the app that will finally put me in the habit of using a to-do list.