Last Ninja 2 is to me easily the best soundtrack ever, C64 version.
Turrican II on the Amiga had some great tunes as well.
Zelda and Mega Man II on NES. Also worth mentioning Rygar, Batman, Metroid, Ninja Gaiden, Tetris and Shadowgate which all had some of my favorite video game tunes too, but couldn't say the whole soundtracks are awesome.
I think video game music got worse and worse the less limitations they had.