If in the Login preferences panel, you have enabled the setting to enter the username with the keyboard, enter ">console" (no quotes) and you'll get to a classic UNIX type login screen.
After you've logged out of this screen, if you press Control and Eject the usual login screen appears!
Probably not that useful but maybe somebody will find a use for it.
[Editor's note: I thought this had been posted here before, but I sure couldn't find it with a search.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020318020806482