Some useful online DNS tools

When I recently moved a few domain names from my web hosts name servers to my domain registrar's (Enom) I found these good online tools for checking the validity of DNS zone files and their propagation:

• Simple online dig tool from Geektools - One of the oldest online DNS tools, but still very useful.
• A slightly more complex one - From Ring of Saturn which allows you to add the same commands as the command line dig tool.
• Nexcess Global DNS Checker - Allows you to see how your DNS changes are propagating around various ISP's name servers.

And finally:

• Centralnic Domain Doctor - Performs a full diagnostic on a domain name to identify any DNS issues.