Many of the early Masters of Evil, and the older villains who've kind of faded into obscurity. Like the Melter. Sounds dumb, but he can melt anything, just about. But he was too much of an idiot and became entrenched in an "I must beat Iron Man" mentality. He could melt anything! No one could stand in his way if he used this ability with tact, but he was an idiot.
Also the Mole Man, he's content just being smelly and dumb, he could have his moloids dig various tunnels to undermine the durability of entire cities. Boom, New York just fell over, and he reigns supreme.