Best class to dual box?

Whats the best class to dual box besides a shaman?
(cant do shaman because my accounts aren't all BC and I am alliance)

Mage.

Pyroblast -> Presence of Mind -> Instant Pyroblast

It would be nice if the backup guy has healing of some sort. This means Shaman or Druid if you want ranged DPS, possibly Discipline Priest (but wouldn't be my first pick - better DPS on first two), or Paladin if you don't mind dealing with two melee.

For the first...anything is good. Go with what you like.

druid and warlock. DoT & HoT farming

I second the mage call - go fire spec and nothing ever gets remotely close to hitting you :D

Please search, there is even an entire section on class comps.