A simple, but effective and attention grabbing, tie for demos is the Pink Squirrel -- http://www.youtube.com/watch?v=qJQTEsLgcbg. The name and the bright materials get people's attention and it's pretty simple to tie. You can tie it in any size (#12 is my standard for trout). I usually use a straight hook (TMC 3769 or equivalent), a brass bead, a chocolate brown body, and pink Ice Dub for the collar. It works very well for trout and it's also excellent as a panfish fly (even for ice fishing).