Almost all of these 'mandatory free registration' websites let you choose your own username and password, and some even tell you the minimum length on the login screen (New York times, anyone?). The best service you can do is use a disposible hotmail account to sign up with an obvious username/password and spurious details.

Often you don't even need to register, someone else having done the work for you. Mr qwerty, and Dr zxcvb get around a lot. Often Mr Qwerty's account gets nuked, but they often overlook Professor Bvcxz.