Feral Druid and Rogue as partners in crime is very delicious.
Imp. Leader of the Pack (druid) offers you both 100% chance on crit to heal yourselves for 4% of your total health. Since Cats and Rogues carry a high amount of crit, this means you'll both have a higher amount of survivability, and the druid won't have to pop out of form as much to heal when you are duoing. In a group setting, it's even better, as it saves your healer a lot of struggle.
Distract (Rogue) is fantastic for stealth running and duoing bosses or other elites that might be hard to get to. It ensures that both of you will be able to get from point A to point B without being seen so easily.
Mangle (Druid) is great when paired with Garrote (Rogue), because it increases bleed damage on a single target by 40%. This means whatever you're smacking around will go down a lot quicker.
Since bearform druids have a high armor mitigation and stamina, they'll be able to take a licking, and tank many normal world mobs at once, or several elites. The good news is that in a pinch, druids can still toss out a heal or two! If you or your partner is getting low on health, they can pop out of form, heal a bit, and pop back into bear, leaving the rogue to keep damaging and get those mobs down quick.
Regardless of which class you go with, I do not recommend any class leveling as Resto or Holy. It will be very slow going, and healing (especially in lower level instances) is more dependent on gear than on talents. The quicker you can kill things, the faster you will level, and the happier you will both be.
Good luck out there!