Can't really think of any that hasn't been done before, unless you want to make a bartender class, or a barber class, or a librarian class etc. but I doubt anyone would want to play those, at least not seriously. You can mix n' match class mechanics, but I'm pretty sure in this day and age we'd all go "Hey, this is a mix n' match class!" so that wouldn't help much. I'm out of ideas otherwise.