I've just pushed out a release of DNSimple that updates the DNSimple API to add support for domain registration, domain transfer and a variety of template and template record manipulation actions.
The full documentation for the REST calls is available on the DNSimple developer site. Please keep in mind that the new domain registration API calls require immediate payment for a successful registration, so don't go crazy, ok? (Unless you want to go crazy - I won't mind)
In conjunction with the API update I've also pushed out version 0.5.0 of the dnsimple-ruby gem. The source code for the gem is available on Github in the dnsimple/dnsimple-ruby project.
There are still more API calls coming in the future, but hopefully these additions will give everyone more incentive to try out the API and see what they can do with it.