[oscarduignan]

http://orgmode.org/ is a brilliant tool for this kind of thing. And you don't need to know emacs to get started. If you're unfamiliar with emacs then getting it setup does require some persistent effort, however once your over that hill, it's really easy to work with. And I have mine set up so that I can hit a key binding wherever I am and a window will pop up so that I can enter a note or todo item.