I'd like to second nidoking A+. It has a nice movepool, with hazards, strong special attacks, and a few good physical attacks. More importantly, however, it has a great ability, and isn't deadweight- notably, it's a Clefable GSI that doesn't mind Thunder Wave. Quuen would be similarly good, but King is almost always better- there should probably be at least two sub ranks between them.
Lucario is a solid leader, although it definitally isn't S. While it lacks a good ability, it makes of for it with its over abundant priority and boosting options, as well as other common attacks. It can make nearly any non-stall follower work. My opinion is it would fit well anywhere in the A ranks, but that A+ is a better fit.
Breton is excellent- it has a good physical movepool, a decent special one, swords dance and spore. It also has two good abilities in poison heal and technician. Im not sure where it belongs, exactly, but it should be fairly high up.
While Zoroark may look gimmicky, it's ability is top notch for stallbreaking. It also has boosting on both sides as well as the godlike knock off, and gives a lot of Pokemon exactly what they want, most notably Gengar. It is a bit of a one trick pony, but it's a really good trick- somewhere about A- or B+, I should think.
Mawile and Corsola are good leaders as well, but they are a bit lackluster Pokemon themselves, which does hurt. Mawile almost certainly belongs in the A ranks regardless, but Corsola will probably have to settle for B- or thereabouts.
Arcanine is fairly solid, as most extreme speed providers are. It does have two good abilities and reliable recovery, which might make up for the lack of hazard removal and boosting. It can definitally provide a nice balance build- Intimidate Hippowdon and FF Skarmory, for instance, are great pairs, especially with will o wisp, while pin sire can sweep with extreme speed.
Additionally, I think the S Rank itself is a bit over large- Clefable, Dragonite, and Kecleon belong there, but are mew and Sableye really that amazing? Don't get me wrong, they are solid picks, but they seem to fit A+ more than S.