A normal looking helmet, the type worn by most armored individuals.  A aura
of alteration magic can be found if it is looked for.

When placed on a person's head, this help will polymorph the wearer into a
different race.  The DM can either pick and choose the race, or roll
randomly on the following table.  Other than this the helm provides a +2 AC
bonus as long as it is worn.  Once the magic of the helm has worked on a
person, it will never again work on the same person.  To remove the effects
of a Helm of Shape Shifting, a remove curse must be cast by a 12th level or
higher priests.  Note that any person changed into a race that is not
allowed the class that they are, will not be penalized in any way.  (In
other words, what a dwarvish mage -- here you go!)

01-15 Dwarf
      1-3 Mountain
      4-6 Hill
16-30 Elf
       1-3 Moon elf
       4-6 Sun Elf
       7-9 Wild Elf
       10   Drow elf
31-40 Human
41-55 Gnome
       1-5 Forest gnome
       5-9 Rock gnome
       10 Sniferveblin (or however you spell it)
55-70 Halfling
      1-3 Stout
      4-6 Tallfellow
      7-9 Burrfoot
      10 Leiran
71-85 Orc
86-90 Goblin
91-93 Hobgoblin
94-96 Ogre
97-00 DM's Choice

The first record of this helm appearing was in Myth Drannor when the famed
bladesinger Alkella Quickblade was transformed from a gold elf into a human.
The bladesinger continued to function just as a elven warrior/mage, but the
shame of being a human drove the elf into voluntary exile.  He was never
heard from again.