Mozy Remote Backup give you 2GB of free online and secure backup. When you sign up for the service, you then download a client that automatically backups folder you specify. There is currently only a Windows client, but Mozy promises a Mac client is on the way. What happens when you exceed 2GB? Well you can upgrade your account to a paid account that gives you a whopping 30GB of storage for only $4.95 per month!
UPDATE: The service is advertised as free storage, but they do send you a weekly email with links to relevant sponsors. Still, it seems like a small price to pay.