For some really hard-to-find stuff, check out these guys: Fly Tying Feathers, Furs and Equipment. Everything for Classic Salmon Fly Tying.
(I have admired their wares at fishing shows, but have not bought from them.)
+1 for Bear's Den, Stone River Outfitters, and Feather-craft.
Mike Hogue maintains a good site at www.eflytyer.com
Anybody else miss Reed Tackle?
Will E. Hille ever get back on their feet after their fire?