RMx = Rogue, Mage, x. You'd be swapping out the priest (normally RMP) for a MW monk. You're dropping fear which is a big loss, because RMP relies heavily on a strong opener forcing lots of CDs, and without fear you might not force as many trinkets/etc as you'd like. Still a strong comp in 5.2 though.
FMx = Feral, Mage, x. Normally works with a Priest or Shaman, sometimes with a Paladin. The strength of this comp is that the MW monks incapacitate wont DR the sap/gouge from the Rogue. The leg sweep won't DR the redirect kidney/cheap and the Feral doesn't need freedoms etc, which monks cant provide. This will be really strong for you guys.
MLx = Mage, Lock, x. This will be pretty strong in 5.2 too. Lock can play Affliction or Destro and the Mage can play Fire or Frost and this comp can play completely different strategies. Currently Frost/Destro is best, but Affli/Fire can also work for a pressure comp. MW monk heals will be able to keep both up, and the lock can sacrifice an imp to keep the MW monk out of CC.
Shatterplay = Spriest, Mage, x. Will be really strong in 5.2 still. Both mage and spriest have good survivability and do a lot of damage. People are saying Spriest will be the strongest caster in 5.2 so this will be a good bet.
Spicychicken = Boomkin, Mage, x. Usually played with a priest again, for the fear, although leg sweep could be really strong for this comp. Will be pretty viable in 5.2. Mage can play Fire or Frost for this comp.
Other possible comps: Warr/Mage/x, Hunter/Mage/x and Ret/Mage/x, although these will all be sub-par.
In order of best to worst (in my opinion):
Mage/Lock = Mage/Spriest > Mage/Feral = Mage/Rogue > Mage/Boomkin >>> Rest