CDC and Elk was my best fly last year on the Don, a real 'confidence' fly. Great for 'sight' fishing but also very effective for fishing 'blind' in likely places when no fish are rising.
I think the original designer Hans Weilenmann prefers (coastal) Deer Hair for the wing rather than Elk ?Tying is here
http://www.danica.com/flytier/steps/cdcelk/cdcelk.htm? I have tried all sorts including the Elk and they all work great, but prefer finer deer hair, usually avialable at Orvis Banchory or from Phil at Fly Tying Boutique. Like on my DHE's I prefer light coloured hair as it is easier to see especially in low light when this fly becomes really deadly (IMO). Mike used to sell CDC or if not now, Orvis CDC I think is pretty decent. A size 12 (!) Barbless Partridge SLD produced a 3 pound plus Brownie in June - fished 'blind' through a likely run
. I lost bigger fish....always next year. There are some interesting 'variants' including a crippled version, and tying them on curved hooks as well ala DHE.
Awesome fly. Possibly not as deadly as DHE on it's day, but much more versatile as you can fish it up, up and across, across and down and even let it 'swing' (Sea Trout will go nuts for it !). When it swings in to your bank down stream from you strip it in for a bit especially at night - I am sure fish scoffing trout take it as a minnow as well.
Lindsay