Ninja Gaiden 4-2 is my favorite on the NES by far. That is a great tune that isn't even dated, really.
Some that instantly bring me back to childhood:
Was so happy to beat rygar the first time since it didn't have a save feature and it basically required you keeping your nes on for hours and hours. lol.
TGL, awesome game! (And some of the most awesome remixes on OC Remix too)
And most unknown (but good soundtrack) goes to King's Knight, which is one of Squaresoft's first original games ever I believe (or at least one of their first).