dns@insidesystems.net is a free, fully-featured DNS hosting service with a flexible API that can be integrated with billing systems, monitoring systems, or anything that can use a browser or speak XML.
Yes, that's right. Free DNS hosting, for anybody. Even you.
Just signup, make a domain and add some records to it. Then tell your registrar that your name servers are: a.ns.insidesystems.net, b.ns.insidesystems.net, c.ns.insidesystems.net and d.ns.insidesystems.net.