I would go for at least one class that can rez/prevent a wipe. Dual locks with SS, or any healing class. I think 2 druids would be nice. Make them both feral, one bear tweaked one cat tweaked. Or make em both moonkin. Shaman could be cool too. If you don't want em both elemental, make one enhancement to 'tank'. Twin paladins would be fun, one prot/ret and one holy/ret. You can basically take the 2 talent trees and make them compliment each other. Rogue and Druid would be interesting, dual stealh runs!

Basically anything you want! And leveling up will be pretty quick, less worry about collection quests, and you still kill pretty quick.