Theamhdaigh, I think people aren't answering because they're not sure what you want. BMI, as well as ASCAP, Harry Fox and others, are agencies set up to protect musician's rights.

A publisher is something quite different - whoever publishes a song book, recording, sheet music, etc. (I think "publishing" also includes web pages, but I'm not sure.) I believe quite a few songwriters are publishing their own works these days - it sure beats paying someone to do it unless you don't mind spending the money.