Ostrich herl is a great fly tying material. It can be used for an abdomen with pulsing gills or a lively thorax area. I have used it for the tails on The Orb.  It comes in assorted colors and barbules lengths.

Ostrich Herl Thorax & Ab w/ Krystal Flash Rib (SwittersB)

The Orb (Callibaetis Emerger)