One of the most useful apps I've encountered in the last few years is Evernote. It has a bunch of handy features, but essentially it's a internet accesible, synced, notebook system for your computer, mobile and web. There are native clients for Blackberry, iphone, Palm Pre, Mac, and PC, but the app's core function is available for any single application that is internet or email capable. The website itself allows you to view and edit all your notes, full functionality, and you can set up an email address to email notes too.
I currently have an android phone, so to take notes I use the email address post method. One really awesome feature that evernote possesses is that it can search the text inside of images. So you can scribble down some notes on a knapkin, take a cellphone pic, and email it to your evernote account. Although it won't convert the whole image to text, you can easily find the note you wrote about "buy a new camera" by searching for "camera."
I use the app as a universal capture for things I need to remember no matter where I am. Whether I'm on my computer, walking on the street, on somebody else's desktop I can access my notes and keep track of numbers or ideas. Whiteboards, napkin breakthroughs, notes from borrowed paper, posters for design inspiration, jotted down Wifi codes... it's all available and easy to access from everywhere.
Evernote is free with ads on the clients and site, and up to 40MB per month upload from your various clients, which I have found to be sufficient so far. I highly recommend using it, it's replaced and consolidated the way I remember small items and ideas throughout my life.
