There's approximately 745.3 Dark Lords in literature and pop-culture. I'll give you a run down of three (with a special guest at the end,) in order of creation.
Lord Sauron.
AKA: The Lord of the Rings, The Enemy, The Great Eye, The Dark Lord.
Traits: Bizarre ring fetish, kickass Mace of Pwnage, kickass minions of pwnosity.
Darth Vader
AKA: Anakin Skywalker, Lord Vader, The Dark Lord,
James Earl Jones.
Traits: Lightsaber. Hell, everyone loves lightsabers... THE FORCE! Quotability to the max.
Lord Voldemort
AKA: You Know Who, The Dark Lord,
He Who Must Not Be Named, Tom Riddle,
Ralph Fiennes.
Traits: Bitchin' snake familiar, Near immortality due to splitting his soul, uh... cool eyes?
George W. Bush
AKA: Dubbyuh, Bushy, Bushy junior.
Traits: Horrible public speaking skills, inheriting the uncanny ability from his father to bring war to America, funny, sticky-outty ears.