Two Cheapskate Freelancer readers recommend MozyHome Free, which gives you 2GB of storage online at absolutely no charge.
You simply set up your account, download the software, and Mozy will backup your files when you’re online.
I’m actually a former (but pleased) Mozy.com subscriber at the $4.95/month level, where you get unlimited storage. When I bought a new computer, I switched to Norton 360 backup (and I’m really not a happy customer. I should switch back).