Really anything can work in 2s. I am playing ret/rsham which seems to work OK. First week we went 19-1, next week we went 7-6 (2 draws so 7-4). We haven't used any voice communication, so I think it would do quite well if we actually spoke and coordinated.
Ret seems very strong right now with off healing being buffed so much. I'm more interested in 3v3 comps with ret. Any partner with a slow and a legit CC would be a good DPS counterpart, then a healer with non-DR cc. Maybe Ret/Rogue/Disc or Ret/Mage/Resto sham/druid. Ret/DK/any healer probably works.
I have an opinion of a class that goes well with retri, but it's not always the most popular, running with a warrior in 2v2s let me win nearly almost every battle, if you get the right burst combos at the right time you can easily pile the pressure on any combo, the burst from a warrior and paladin combined with all CDs popped renders them unable to even think.
Saying that, you don't have a lot of control, I mean you have your basic stuns/slows but other than that, the lack of range can be a problem, especially if you come up against fear-heavy opponents like SP/Lock.
All seriousness Ret/FDK if you wanna run melee and own. Just hope you don't face a holy pally. as far as viable dbl melee comps. Ret/Rogue Scooby Doo cleave is probably pretty strong right now considering rogues got HUGE buffs. other than that Ret/Spriest is really good Ret/FMage is OK. Best Two's comp is honestly Ret/BM. Unreal Burst insane CC only from hunter and utility from the pally makes it a hard comp to counter and easier than normal to win with