Dropbox - Online Sync and File Sharing
ownCloud - ownCloud is an open source project enabling businesses to host their own cloud storage while maintaining regulatory and compliance needs.
Mega - Secure File Storage and collaboration
Google Drive - Access and sync your files anywhere
FileRun - Beautiful, fast and reliable selfhosted file sharing and sync.
Sync.com - Sync. com offers a backup tool and a file sharing service, rolled into one.