In my own oppinion and class could dou with a ranger. The massive DPS that a ranger puts out can eliminate the need for a tank if you are just Duoing.
But personally i think that something along the lines of a druid would be great. With there HoTs and there decent DPS, I think the Fury would be a great match with a ranger. But like i said, pretty much an class would be able to pair up with a ranger. I do think that 2 rangers could work out great because of the massive dmg the 2 of you would be doing, but just note that if you are fighting a Heroic ^^^ mob that cons close to your lvl or higher you might be in a little bit of Health trouble. Where as with a fury you will have better dps that all the other Healing Classes but also the ability to heal your friend.
Or, if you want to go with a fighter class. I think that a Pally would be a great pair do to the fact that they can heal them selves, ward them selfs, buff, and from my personal expeirence they are the best tanks HP and keeping agro wise do to the decent heals and the self wards.
hope this helps any... Keep us posted on what you do decide and how it works out in the long run
:)