I recently came across Jungle Disk.

They use the Amazon S3 storage system to provide you with a secure way to store files over the Internet, using Amazon for the storage and their software as the interface between your machine and Amazon. Primarily this is practical for use in a backup situation, and there are a number of benefits to this approach; for one, your backup is kept securely off site, and the data is encrypted too.

The cost is low too - 15 cents/Gigabyte, which compares favourably to similar services, like GoDaddy and Apple's iTools/Mac.com service. Ironically for the latter, because Jungle Disk appears as a local disk, you can use the Mac Backup application to store your files on the remote Amazon system.