Looking for dual-box combo suggestions

[myrddin]

I have been contemplating starting up wow again - wondering about suggestions for a 2char leveling combo - I have only ever multiboxed in a raid / BG environment, so my experience doesn't really help me too much.

I have been debating between the possible duo's of lock / druid / DK - I have a bt/sunwell geared druid and lock that I used to play together as healer/dps in our raids, and leveling a DK wouldn't be too hard to catch up and then pair with one of them as an alternative maybe?

Playing before, I used to find playing a healbot with a ranged dps char was fairly easy - main-screen was the healer, and I setup threat meters to show my warlock on the druids screen (so it was very easy :P) *but* the idea of leveling up a DK to tank, and then leveling via instances as "dk tank+ druid healer lf3m dps" has its attractions too.

Really, I want something that will get me to 80 relatively quickly, and be a viable combo to use for most raids - whatever spec works best. Any recommendations?