This was proposed during Tornadus-T's reign but the discussion kinda just fizzled out so I would like to repropose this:
Landorus to S Rank
Special RP Landorus is one of, if not the, best sweeper in the current metagame. This thing is so ridiculously powerful that with Sheer Force and LO, it hits around 610 Special Attack, while still retaining the ability to change moves. Ground also has excellent neutral and super effective coverage in the meta, hitting many specially defensive walls such as Jirachi really hard. It also has an unorthodox yet weirdly effective set of coverage moves. Focus Blast deals with Skarmory and other levitating steels, as well as dealing heavy damage to Rotom-W and the like. While HP Ice is incredibly good for sweeping weakened teams with Dragons and Grass types on them, I've actually been using Sludge Wave over, and I must say that it is absolutely amazing. Landorus can do upwards of 80% to Defensive Celebi, one of its best counters with any other move. It can also 2HKO Latios after rocks. While Poison is kind of a terrible offensive typing, it lets Landorus have a neutral coverage move that can be helpful in many situations. What I described above makes Landorus sound like a generic superpowerful mon with no coverage, Landorus's ridiculous ability to both wallbreak and sweep is what makes the special set so good. I mean, it can 2HKO Blissey with a non-STAB Focus Blast after SR.
While Landorus's special set is the best set and the most common one as well, the fact that it can still run a variety of extremely effective physical sets is what pushes it into S-Rank. Say you switch in your Celebi or Latios to take a hit, but then you get hit with a Scarf U-Turn. Its still one of the best revenge killers on sand teams with its physical scarf set. And to add to this, it can even bluff that set with an Expert Belt set. Finally, it has different varieties of Swords Dance sets, such as SubSD and SD+3 Attacks, that are still viable, though not as effective as in BW1. Landorus is such a powerful and effective pokemon that I think it deserves S-Rank. Many people even feel that its broken, which while I might not agree with that, still attests to its effect on the metagame. Its ability as a late game sweepers is unsurpassed in terms of the current metagame.
P.S. Don't use Timid on Special Lando
EDIT: I forgot to talk about tons of other options on a few sets, such as Substitute or U-turn on the special sets, but I think this simply further supports Landorus' insane versatility.