“Getting Things Done” or GTD to its (sometimes cultish) followers is a time/action management system put together by David Allen.
The core strategy behind GTD is to get all your tasks out of your head and onto paper/computer/pda/whatever. So rather than keeping multiple to-do lists scattered around plus trying to remember a bunch of stuff to do, you get everything written down in one place and you can focus your mind on actually completing tasks.
Next you avoid handling these tasks multiple times. When you, for example, get an email, if you can complete the request in under two minutes then you do it immediately, if not you put it on a to do list, or delegate it, or delete it. No more keeping hundreds of emails just sitting in your email box that you occasionally scan over and consider doing something about.
Michael S. Hyatt has written extensively about his experiences with this system, here are a series of his posts. If you find this stuff interesting or helpful then there are many more resources scattered about online.