Here are some productivity tools that I find invaluable to staying organized:

Deferred Sender allows me to send emails to myself in the future as reminders.

Dropbox allows me to use drag-and-drop to sync files between computers.  One can also access, upload, and download one's files over the web interface.

Evernote is note-taking software (there's a web-based version too for when one is away from the computer) with its own built-in backup.  Your notes are preserved on their server as long as you like.  You can add PDFs which are then scanned and become searchable.  There is a version available for mobile phones, too.

KeePassX keeps all my passwords secure and organized; I have access to them under one master password.  Available for all operating systems.