I have always greatly admired people with a natural flair for organization; unfortunately I am not one of them. For the rest of us, there is org-mode. And what might that be? I hear you say.
Org-mode is a customization of the powerful, and programmable, text editor Emacs. Don't be misled by the "text editor" label; Emacs is to text editors as Ferrari is to cars; except that Emacs is free. More aptly, perhaps, it could be characterized as the Swiss Army Knife of the digital world, being adapted to everything from software development to playing music to composing email.
For me, however, the killer feature is org-mode. Org-mode takes simple text files and turns them into a full-fledged personal planner, and it is completely customizable! The down side is that, while org-mode is simplicity itself to use, it can be the very devil to configure (the price of complete customizability). Forturnately, there is plenty of help online, such as Bernt Hansen's excellent web page. So if you have the time, patience, and determination necessary to assemble a first-class organizational tool, download a copy of Emacs and org-mode and have at it!