(You): Is there a free DNS service (like mydomain.com) that has an API that lets me change nameservers/A records/etc via command line?
(Brett): zoneedit has this service. Check this link, see if it helps:
(Brad): Zoneedit.com allows you to make some changes over HTTP with basic auth, so you can use something like wget to call these changes.
[Vark assigned category: API, more details]