Brassie

Size #18 Brassies; left - copper; right - chartreuse

The Brassie is one of those nymphs you simply must have as a trout fisherman. Copper by far has been the best producer personally, although most any color works at certain times. Also one of the easiest flies to tie:

Hook - Curved Shank Caddis
Thread - 8/0, typically black
Body - Fine Ultra Wire
Thorax - Peacock Herl