If you go to https://www.facebook.com/settings?tab=applications https://www.facebook.com/settings?tab=applications you can see a list of everything you've signe

If you go to https://www.facebook.com/settings?tab=applications https://www.facebook.com/settings?tab=applications you can see a list of everything you've signed up for using Facebook OAuth, then determine from there what sites you still use and adjust logins as necessary