Very useful guide on how to setup dnsmasq on OS X. Weird stuff with /etc/resolver/tld whereby the resolver is only used for a particular domain. Useful in some ways, weird in others.
Really detailed tool that diagnoses in great detail each step of the DNS resolution process for a domain. Free and invaluable.
Really helpful explanation of glue records (whereby the root servers return the IPs for some of the TLD servers to save a lookup, and allow the system to work).
Check DNS resolution speeds from various places around the world, very useful.
Free domain names (without DNS) on the .za.org and .za.net subdomains. Requests require human approval and so can take a few days. Interface is plain text to email, old school!
OpenDNS is a free DNS service (I'm guessing) which filters sites based on pornographic and other types of content. It also corrects errors (.cmo instead of .com, etc) and lots of other things. The service is ad funded.
Dynamic DNS and DNS hosting from DynDNS. Starts at $25/year/domain for standard DNS.
DNS hosting and other services from EasyDNS. DNS hosting starts at $20/year/domain.
DNS Hosting from DNS Park, starting from $10/year/domain.
Free primary and secondary DNS services for individuals / small businesses from xname.