Here’s a list of the common applications I use:

• Dropbox – stores your files in “the cloud”.  You can read my review here, or sign up for an account as a referral  here.
• EverNote – this is a great tool for note taking.  I use more than one PC/Mac – basically multiple computers.  Evernote let’s me capture text, images, web pages, all sorts of things and automagically share them between machines in the same way Dropbox shares files.