If you're only doing 2, Affliction locks is a pretty good idea. Running around with a couple pets and some insane dot's, you'll do pretty well.

For 2 boxing, pretty much anything will work.

-2 hunters (pets to tank, traps, ranged DPS)
-2 mages (POM Pyro x 2, Ranged, AOE)

Those would be my choices though. Shamans aren't THAT effective unless you're 5 boxing them