I am gonna say HTC's tablet or Xoom will be number 2, either sporting Android of coarse.
My logic on WebOs and playbook is they will be like WP7, too far behind to catch up anytime soon.
You cannot count phone apps. So, Web os, playbook and android are in the same position. Although, android does have an advantage of followers from the phone market. So, does blackberry, but they are defecting, though.