SpiderOak makes it possible for you to privately store, sync, share & access your data from everywhere.
BitTorrent Sync is a peer-to-peer file synchronization tool. It can sync files over the Internet via allegedly secure, distributed P2P technology.
Google Drive is a file storage and synchronization service.
More meant as a back up solution, it may also provide ways to sync files while going through a may be somewhat less trusted central server.
OneDrive is a file hosting service that allows users to upload and sync files to a cloud storage and then access them from a Web browser or their local device.
Wuala is secure cloud storage, a haven in the cloud to store your files. You can safely access and share your files with friends, family, and co-workers.