Google (and other sources) usually point to the Karakoram Highway as the highest highway in the world, with its highpoint being the Khunjerab Pass at around 4,700 meters. It's Wikipedia entry covers its ass by calling it the highest "international highway."
But the Tibet Friendship Highway runs through two passes claimed to be over 5,000 meters and long sections are at over 4,000 meters. The Friendship Highway is just about completely paved now, so it would seem to be the winner.
Am I wrong? I guess I should cover my own ass by saying I'm referring to the highest highway, not highest paved pass or small stretch of road, in the world.