How do I delete cookies when users log out? How do I delete cookies when users log out? How can I do this with out modifying any core module?
Imlement hook_user_logout($account) and call user_cookie_delete($cookie_name).

For example:

function mymodule_user_logout($account) {
  user_cookie_delete('name');
  user_cookie_delete('mail');
  user_cookie_delete('homepage');
}