If you want the smogon Uber tier, then I believe that so far only Hydregion, Blaziken, Reniculus, Pokemon with the ability Inconsistent, and all instant weather setters besides Abomasnow. The reason for this: smogon sucks at battling. They can't seem to beat these guys for some reason. I for one can take these weaklings down with ease.
If you want to know which non-legendaries are banned in my tier, which is the one used on Pokemon Online by us when against each other, only Wobbuffet, Wynaut, and Shedinja are banned.