BuddyPress.org

Alrighteethen, I’ve given up on a reg form on a custom login page.

Even simpler, from a code standpoint is a message on the login page that says “This is a private site. To join, please email the site administrator.” with a spam-proof mailto link. I can then manually sign them up. Pretty clunky, but it sounds like BP will be better at this kind of thing someday soon.