Notational Velocity - http://notational.net http://notational.net, mainly because it's very easy to add a note in a few seconds using only the keyboard. I've t

Notational Velocity - http://notational.net http://notational.net, mainly because it's very easy to add a note in a few seconds using only the keyboard. I've tried a lot of note taking software, and this just stays out of your way. Also, it's open source.