In my campaign (
http://games.groups.yahoo.com/group/DnD3VanishedLands/), Orcs look like what one role-player once jokingly called "green gorilla lizards." Descended from Ru'ulok, the same root stock of Ogres and Bugbears, the Orcs of Zuromm are about 6 feet tall, muscular, with simian build and facial features. They have greenish skin and sparse black hair, as well as red eyes with yellow slit pupils, pointed ears, and fangs. They tend to wear black Roman-style armor and carry scimitars (thanks, Ral Partha), although they aren't always evil.
I was never a fan of the "Star Wars" Gamorrean guard-style porcine Orcs that have appeared on and off in various D&D editions, and the Orcs in my setting are somewhat more reptilian, although not as much as the doglike Kobolds or Sleestack/Scarran-like Lizard Men.
The "high Orcs" (inspired by J.R.R. Tolkien's Uruk Hai), not unlike Half-Orcs or Hobgoblins, are more human in posture and are more organized and clever, using things such as ambushes and blasting powder in their strategy. In general, Orcs are still a twisted reflection of Elves, while Goblinoids are more the opposite of the hill peoples (Dwarves, Gnomes, and Halflings) in my world.
I agree that Claudio Pozas' art is excellent, and I was also inspired by early Larry Elmore posters for D&D, as well as the evil green humans mutated by the Loc Nar in the original "Heavy Metal" movie. As for "Star Trek's" Klingons, their combativeness and sense of honor has been more of an influence on my Mountain Dwarves or Hobgoblins than on Orcs... In my "Vanished Lands" setting, Ogres have tusks, and Bakemono (eastern Goblins) look like pigs.