Check the Titus web site. I belive the Racer X comes in an XXS. I'm just under 5'4" and can't say enough about my Racer X. It is an awesome bike and I've gone through a lot of them. Sonja (my Titus) will climb hills with or without you and is incredibly nimble on singletrack. She's a really wonderful bike.

You've hit the two that I would have thought off the top of my head. Does Ellsworth or Ventana make anything in this size range?