Apple's iCloud went live today, meaning if you're the owner of a Mac computer and/or iDevice(s), you can now start syncing your docs, photos, contacts, etc. to the cloud for free.
iCloud comes with 5 GB of free storage, and stuff that you purchase from apple, like music from iTunes or apps from the App Store, will sync across your devices without counting against your storage limit.
To use iCloud, you'll need to update your iDevice to iOS 5 and your Mac to OSX 10.7.2, which you can do from system preferences. Read more about iCloud here.