I'd personally go Rogue/Druid. Mainly because you can stealth anywhere together and because the Druid is so versatile. You can spec as Resto and also add some dps or spec Moonkin and toss on an occasional heal. Thorns, MoTW and Faerie Fire are all nice additions.

Druid/Pally would be my other choice (Feral & Holy, respectively), due to nice synergies.