Any serious online business knows that good web hosting is important. But beyond selecting a good host, it is also important to make sure that your web host is doing their job and to make sure you are alerted the second your site is down.
Pingdom is a great tool that will do both of these things. You can setup a free account that lets you monitor one website, or you can go with one of their paid plans and monitor up to 30 different sites or servers. If your website in unavailable at any time, Pingdom sends you an alert letting you know the site is down. You will also get an alert when the site is back up. I elect to also have a monthly performance report sent to me via e-mail.