We now have two unknown cheats. Email me if you find out what any of them do, or, you can sign up at our forum and discuss it with other GTA fans, in this topic.
Bones from GTAForums discovered that unknown cheat #2 makes prostitutes pay you (rather than take your money). edisoncarter confirmed that unknown cheat #1 does infact do nothing at all.
Related Links: edisoncarter's site, GTAForums