Many top-level cloud backup providers offer free storage solutions. Dropbox, SugarSync, CloudDrive, Windows Live SkyDrive, MemoPal, ADrive, and IDrive are just a few providers that offer free cloud storage backup accounts.
While all of these companies provide excellent free service, the main problem with the free versions of their products is that they are seriously limited in terms of how much service they provide. Most only provide between 2-5GB of free storage.
The exceptions to this are Windows Live SkyDrive, which provides 25 GB of free storage and ADrive, which offers a whopping 50GB of free cloud storage backup.