Useful and Free:!

Dropbox is an application where you can automatically synchronize your files between computers (any mix of Mac and PC), mobile phones, and the web. It is a free service that provides 2 GB of space. You have the option to pay if you need more space.

I love how seamless and easy it is. I just drop the file in my dropbox folder and it syncs to all locations. It is a great way to backup important files automatically and you will always have your more current changes everywhere. It takes out a lot of legwork.

Never be without an important file again!