Dropbox

Dropbox is an easy way to store, synchronize, and share files online. The free account gives you 2GB of storage, and you can pay for more if you need it.

What makes it cool is how easy it is. Create an account on their website, download and install the application on your computer. Dropbox will install a folder on your pc and you're all set. Want something backed up just copy it to the Dropbox folder. You can access the files in the Dropbox folder from anywhere just by logging into the Dropbox website.