If you remember an old geocities username exactly, then you can just try to go to the website "**.oocities.com/**username" without searching or looking through the lists.
Also when you remember the username but cant find anything then try: web.archive.org
and geocities.ws and reocities.com/...
(The google search above includes results from oocities.com/org, geocities.ws, reocities.com, internetarchaeology.org, webcitation.org, deletedcity.net. Google is not aware of everything avaiable but major parts except for web.archive.org which is not in google.)