QuickDNS is a project mainly written in RUBY and OBJECTIVE-C, it's free.
Quick DNS changer for OS X. See the following link for a precompiled binary...
= Quick DNS
QuickDNS started out as a quick ruby script (quickdns.rb) to quickly modify the DNS settings on my Macbook's Airport network interface. The quickdns.yml file includes the DNS preset options.
= Usage
Usage: quickdns.rb [options] -s, --service SERVICE Set AirPort DNS settings to this service -l, --list List the available DNS services -d, --dns List the current DNS settings applied to your AirPort -h, --help Displays this screen
= Quick DNS GUI
After hacking up the above, I thought it'd also be fun to play around with RubyCocoa to build an OSX GUI version of the app, mainly so I could quickly load quickdns with something like Quicksilver to change my DNS settings. If you have RubyCocoa set up and working (I've been using OSX' Ruby 1.8.7) you should be able to build the GUI version by running "rake".
To modify the available DNS settings explore the Contents within the app and modify the quickdns.yml file inside "Resources".
= History
Version 0.1 of QuickDNS has been around since around May 2011