I wrote about Evernote some time ago, and while I haven't used the tool in a while, they are back with a new version (beta 3.0)
Evernote is a note taking and capture application - by "capture", I mean you can pretty much dump any kind of data (handwritten, images, web, email, etc) into it, and it will track it for you like an electronic notebook.
The new beta is very impressive - it now finally runs on a Mac, but even better, can also run over the web - for full sized browsers as well as little ones like on the iPhone. All of your data syncs automatically - make a change on the Evernote client on one PC, and it shows up on the web, and the Evernote client on your Mac. It works great.
The beta is closed right now, but I have a few invites. Please feel free to drop me an email if you'd like one.