Oh man, Mega Man music is quintessential NES music. I have a strong affinity for
Mega Man 3's soundtrack, since it has a great jazzy quality. They all help define that NES sound, showing what the hardware was capable of (despite the technical limitations). I consider 2, 3, and 5 to have the best soundtracks, but I tend to go to bat for all six of them.
Outside the NES,
Panzer Dragoon Saga has some really serene tracks that are worth checking out. I do appreciate
Grandia II's and
Eternal Sonata's OST's, especially the battle themes. You can never go wrong with any of Nobuo Uematsu's work throughout the
Final Fantasy series (1 through 12). The Super Nintendo is loaded with great works from Squaresoft alone, from
Secret of Mana to
Super Mario RPG to
Chrono Trigger.
Xenogears is another unique soundtrack that deserves a mention.
To do right by my avatar's Custom Title, I'll throw in the Bubble Bobble theme. Just like browsing
Wendy Menus before deciding what to order, I enjoy revisiting old favorites, but I bet the NES version's rendition sounds like nails on a chalkboard to the uninitiated.