A Paladin is nice, because they can heal in battlegrounds; although I'd probably be more inclined to have a 5th Shammy in BG's or just four in Arena... along with someone else playing last slot as the healer.
Pallies can tank, in instances or heroics.
My spacegirls really liked having a Paladin along for a lot of their adventures.

A druid is an option too.
Because a Feral can tank as well as a Prot Paladin.
And you can heal as a Resto, or nuke along with Elementals as a Boomkin.
Boomkin adds the extra spell damage taken.
And Travel Form is very similar to Ghost Wolf.