Currently I own and maintain some domains. For these domains you need a DNS-server to make a proper translation from hostname to ip-adress.
blog.adslweb.net -> 22.214.171.124
But to keep redundancy it is smart to have some extra DNS-servers configured. So I setup a 'master' DNS and a 'slave' DNS, but both of them were connected to a server on a ADSL line... This might not be a big problem, but due to some problems recently, I preferred to have something somewhere else
After some Google-ing, I found Twisted4Life, if you create an account, they provide you for free a 'slave' DNS.