Thousands of small business webmasters briefly lose their domain names at expiration, due to a simple lack of understanding about the roles of three key players in the drama: domain name registrars, web hosts and internet service providers.
One simple solution is to extend domain registration for the maximum ten years. The other solution is to treat domain registrar data as the critical business element it is.
People rarely realize how important it is to keep their domain registrar notified of changes to their email address and and other contact information. The registrar will send renewal notifications to the email address last on file.
Since many registrars honor a 30 day "redemption period" allowing expired domains to be redeemed, it may be possible to save the registration.
Photo by jefras.
1&1 has $5.99 domain names with an automatic renewal and hosting. As many commenters have pointed out here and on Lifehacker, it's typically best to both host your website and register your domain with the same company, as you're less likely to loose your domain.