The Boudreaux pattern is THE ONE fly for all freshwater.
See http://www.flytyingforum.com/pattern7515.html

So far, on this fly pattern, I have caught bluegill, redear, warmouth and green bream, plus bass, catfish, gar, shad, rainbow trout, brook trout, crappie and white (sand) bass. Kinda sorta qualifies as THE ONE, huh?

It can be tied in many colors and sizes, and I would bet a large version would work for muskie and pike.