Zend_Whois
Alright guys, today I've submited my CLA to Zend, and I'm going to make my current Whois class compatible to publish it as proposal for the Zend Framework. With this class you can query for nearly any hostname, fetch the response and check, if the domain is available for registration.
If the proposal passes the review, I'm going to write more classes for the Zend Framework soon.