The Dot-MP Registry is giving Free Domains on their OPENSOCIAL ID Platform.
It is based upon invitations. You need a beta code to register.
Or Register at www.chi.mp for the newsletter. They occasionally send out the codes. It is similar like Facebook,Orkut where you can add friends, stay updated with their activities, wall posting,etc.
Check out mine: www.orkut.mp
Note : I am giving out codes. So the first person to contact me would get a free dot mp domain.