Google Drive - Access and sync your files anywhere
Dropbox - Online Sync and File Sharing
Microsoft OneDrive - Secure access, sharing & file storage
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
ShareFile - Secure file sharing and sync
ownCloud - ownCloud is an open source project enabling businesses to host their own cloud storage while maintaining regulatory and compliance needs.