I think the craziest road I ever drove on was the one lane, ocean-side freeway that hangs over California's cliffs on the Coast Highway 101. While that got a little intense at parts, it was nothing compared to the terrifying roads seen in this Mental Floss article.
Link
In the winter time my wife refuses to go that route (and fly's instead).
http://www.youtube.com/watch?v=M9g3ASdX6gk