Mac OS X app gDisk turns your Gmail account into an Internet hard drive.
Create file categories in gDisk - like "movies," or "for the office" - then upload files to those categories. Your uploaded files will appear in your Gmail account as attachments to messages labeled yourlabel.gDisk. gDisk is a mighty handy way to store files online and access them from anywhere via Gmail. gDisk is free (though donate to those developers if you use gDisk, will you?), Mac OS X only.
Pssst, Windows users: the Gmail drive extension is for you.
gDisk [SourceForge]