I should have known you would have that function already, but as BOAC suggested, I haven't forgotten my password yet (at least not for this site).
Another site I am a member of sends out an email every month with the user's ID and password. Would that help here? You could also include info on how to change email addresses. If an email bounces, force the user to update it the next time they visit the site. For the ones without email addresses currently, don't let them in until they have centered one or corrected the one you have.
goates