As everyone has mentioned there's way too many to have a favorite but I think several stand out enough to make a top ten list. Or a top twenty. Or forty. How about a top 1000 lol.

Anyways, my pick for the country field would have to be the opening notes and rhythm of Folsom Prison Blues, played by Luther Perkins. There's actually been a few articles written about that, with some folks speculating that Luther may have been the most copied guitar player in the world for a while there. I don't know about that, but I do know I'd like to have a penny for every time that song has been played any where in the world.

R&R

Several by Chuck Berry - my number one pick being Johnny B Goode.
Several by John Fogerty - my fav - Green River.
Several by Roy Orbinson = my fav = Pretty Women.

Ok, enuff for now, but you know, now that I think about it, Pretty Women has to be way up there.

I'd be completely happy if I had just one more guitar.