Dropbox - Online Sync and File Sharing
Google Drive - Access and sync your files anywhere
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
SpiderOak - SpiderOak makes it possible for you to privately store, sync, share & access your data from everywhere.
ShareFile - Secure file sharing and sync
Microsoft OneDrive - Secure access, sharing & file storage