A directory of known free dynamic DNS services is a popular full service free dns and dynamic DNS provider. This unique service allows you to share your domain with the members, and use other domains shared by other members. Active competent technical support staff, and supports IPv6. Great for creating unique vhosts. Business class DNS hosting also available.
Redundant high speed dynamic DNS service. Well tested and reliable/durable. Server monitoring also available.
XName DNS  
Another popular free DNS provider, supports IPv6, and auto-import to migrate from your old DNS provider.
ChangeIP offers dynamic DNS and email services.