David Allen and Getting Things Done - here are a few other GTD and general life hacking resources that I use/read/experiment with/learn from.   Tips, ideas, information and links to useful resources to get you firing on all cylinders:

Productivity Portfolio

Notes on productivity


Zen Habits   ...and for more specific GTD-focused stuff, of the many sites out there, here are a few that I have found easy on the eye and laden with helpful advice...  

GTD Times


…and from the archives

43 Folders