I started out with a mage+druid combo but then decided that I would rather have a rogue + druid first. I would have to say rogue+druid is ownage for several reasons.

1) You have Heals over time meaning you can easily just pop renew on the run and healing never really seems that inconvenient even if your rogue is your main control 90% + of the time.

2) You have double stealth you can easily just stealth through certain areas if your too impatient to clear and head directly to the quest objectives.

3) Rogues damage and stunlocks own period. Your rogue can pretty much handle the dps by himself. If you get your druid decently geared out he can pretty much dps constantly too via wrath/moonfire/starfire. If you get really used to the combo you can even have the druid go into cat form for a rogue sap + druid backstabs. The druid can steal aggro from the rogue quite a bit making the rogue assassination tree very viable as you can constantly backstab for critical damage.

4) Druid buffs and debuffs compliment rogue very well. Faerie fire reduces armor so that rogues can instantly pwn. Rogues also have sap and blind making pretty much any PVE encounter easy mode.

5) This duo will require some careful keybindings but it is very very powerful as I am often taking on 4-5 mobs at a time with ease. The rouge generally is about 60-70% of the damage when the druid is not in cat form. The druid can even overtake the rogue in DPS if you are very good with the double melee.

This combo is just pretty leet.... no downtime, multiple CC, buffs, debuffs, good dps, great survivability, stealth... pretty much everything.

Leaving my mage behind though, may try to dual box him along with a priest however I don't think that combo would be as good due to the squishyness and mana dependency.