I think 2 mages are nice because it makes AOE farming so damn easy. Though I'd be following joanas guide and barely do any AOE. For single target grinding I love playing double melee. 2x feral druid would be great once you hit lvl 20 and get cat form and Feline Swiftness.

For mixed classes, I'd say playing hunter/feral would be sweet. I'd play from the hunters perspective, and use the feral as a 2nd pet.