In a recent article, Walt Mossberg talks about backup services, "These Services Make Backing Up Your Files Safe and Inexpensive". He reviewed two services, Mozy and Carbonite.
Mossberg liked Mozy over Carbonite because it is not limited and more customizable. However, according to Mossberg, Carbonite was quicker and simpler to set up. I use Mozy and it is real easy to use. I like it because you can add storage space as you need it and you can choose which folders that you want to backup. For those of you who are concerned about security, you can pick your own password for security key. That way, you are the only person who can get to the data.
There are some drawbacks. The first backup that you make, especially if you have chosen a lot of files, takes a while. But once you are done with that, it becomes incremental after.
If you are looking for a good, off-site back up solution, Mozy works really well.