The world's quickest DNS hosting company is CloudFlare. They also provide a free plan and are among the biggest DNS hosting providers.
Although you might be more known with Namecheap as a domain name registrar, they also provide some interesting free DNS hosting services that include DynamicDNS.
BuddyNS is a top-notch second-tier free DNS hoster. It ranks among the friendliest and easiest hosting providers too though.
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A free dynamic DNS service is offered by Dynu. Similar to CloudFlare, it provides free and paid versions, with the latter including specific extra features.
Another company that provides free hosting and administration services is Rackspace. Only current customers are eligible for this free hosting service.