1. Buy an Internet insurance policy and make sure your service provider has one also. Often called an errors-and-omission policy, it's offered by American International Group, Lloyd's of London, and other top insurers.
2. Buy a WebRamp or similar device. WebRamp, made by Ramp Networks, will switch your digital subscriber line connection to a 56Kbps connection should your DSL service go down. It's far slower, but it'll keep you connected.
3. Back up your data. Not only should your service provider be using a third-party disaster recovery company that keeps copies of all data, it should also regularly burn CD-ROM disks with your data and send them to you.
4. Have a backup plan for any value-added services your service provider offers, such as accounting. Choose alternate providers that can quickly take on new clients, and make sure they accommodate the format of your data.