I use Carbonite, which costs about $55 a year per computer. I'm using it on my main machine, and my two kids' laptops at college. It's almost essential to have online backup if you use a laptop regularly, and travel with it.

There's no upper limit on storage. I've got about 85 GB socked away.

Mozy is another company. Price is about the same for unlimited backup, but Mozy also has a free version if you use less than 2 GB storage.

The beauty of these is that they will update your backups in real time as long as you're connected to the internet.

Microsoft has Windows Live "Skydrive," which I'm not familiar with, but it seems to be a virtual 25 GB hard drive instead of an automated backup system. I have heard that the interface is a bit complicated. It does have the virtue of being free, and would probably work great for manual backups.