Every fly tier and most fly fishermen know about the supposed fish-attracting powers of peacock herl. Off hand I can think of about a dozen flies that use this remarkable natural material. Here are two examples: one dry and one wet. Both of these patterns are pretty old; the Picket Pin originated in Montana around 1919 and the House and Lot first showed up in the late 1950's.
H and L variant a.k.a. House and Lot
featuring stripped peacock body and a peacock herl thorax