Rock / Flying
Grass / Ice
Rock / Poison
Dark / Fire
Rock/Flying is the only one I see that helps counter an S-ranked mon (Char-X) while not giving a huge free switchin to other common mons like Keldeo (Dark/Fire), Heatran(Grass/Ice), etc. and not just being totally awful (Rock/Poison) against 80%+ of the metagame. Rock/Poison means free SDs for Garchomp Bisharp and Scizor, free Tail Glows for Manaphy, free Stealth Rock/Slack Off for Hippowdon, free Spikes for Ferrothorn... I could go on.