my opinion is that the gamecube controller was the pinnacle of controller design, excluding motion sensing units.
not everyone agrees, of course, but my reasoning is that it included everything you needed for any game you wanted to play until the wii came out. 2 analog sticks ( the yellow stick is analog, despite what some people on other forums tried to argue with me about ), the shoulder buttons had that spring function that clicked when depressed and, while the d pad was small, so is the human thumb.
it had built in shock feedback, you could tell by a simple brush of the right thumb which button (a,b,x,y) you were touching, and it was surprisingly durable and compact.
the only thing i could complain about was that it didn't have the pressable analog stick ( not sure what you call that function, but the ps2 had it ), though i never saw much use for it anyway.
also, i'm a big fan of it in part because it was the controller that i played mario sunshine, metroid prime and zelda windwaker with, and in my opinion the latter 2 games had THE best play control i'd ever seen.