Frank Frazetta is the epitome of Swords & Sorcery art! Some of my favorite orcs were drawn by him (although they aren't really orcs, but it's how I prefer to imagine orcs).
Here's Conan obviously fighting an orc horde!
Conan fighting more orcs!
And you can't forget the subhumans from Fire and Ice! They have an orcy look to them!
These images are burned into my mind when I think of orcs in my rpg world. Sort of aboriginal/neanderthal/mongol barbarians with greyish green skin....I'll have to sketch some up sometime.