Back up your files online and sync them to multiple computers and devices. Mozy offers 2 GB for free and the option to add more through paid services. There are both PC and MAC clients.
DropBox also gives 2 GB free space, just drag your files and folders to the dropbox folder in your computer and your files will get automatically uploaded to the dropbox server. You can use it for Windows, Mac, Linux and mobile.
Skydrive is part of the Microsoft Windows Live suite of services, it offers an 25 GB free online storage. It requires a Microsoft Live ID to sign in and begin using the backup service.
Idrive gives 5GB free space for basic users to backup Online unlimited PCs, Macs, iPhones, iPads and Android devices into a Single Account.
CrashPlan is a backup software that allows Windows, Mac, Linux and Solaris users to back up their data to an offsite computers as well as to attached drives / shared folders.
MyPCBackup offers 14 days free trial. After that period you'll need to pay. Note: It is only available for PC, not for Mac, Linux or mobile users.