We are using internet service called Syncplicity to back up our data. The way it works is it keeps all the data in sync between all the designated computers in our office, this allows everyone to access the same files and see the changes instantly (our designers love this!), at the same time Syncplicity backs up all the data over encrypted connection to their servers. It also lets you access your files remotely and share them with friends. The best part it’s all free!! You get 2GB of space and for every friend that signs up you get a Gig of storage.
There are other backup solutions like Dropbox (also free but you can’t define specific folders). Windows Live FolderShare is also free and lets you sync up to 10,000 files (no back up though).