For as long as you know in your heart that what you're making or doing matters, and, consequently, for as long as you accept and embrace the immutable laws of scarcity, your options for maintaining focus will, like Frank's perfect answer, remain stunningly obvious.
Those are very true observations, but the problem is, how do you care? We're told things like, "do what you love," and " follow your passions," but that's just not realistic in an adult, professional world. Writing code is awesome for the first 10% of a project. After that, it usually becomes a grind to complete all the uninteresting things.
http://www.43folders.com/2010/02/05/first-care
All these little tips and tricks are fine. But they're usually treating the symptoms rather than examining the cause.