I don\'t have time to list all those tracks that I think are great (which is a huge list), but I will mention highlights--games with a number of great tracks:
Mega Man X (especially some Maverick stage themes)
some Maverick stage themes from Mega Man X2
Mega Man X3 (especially some Maverick stage themes and the final battle and ending)
Mega Man 6 (Robot Bosses)
Mega Man 5
Star Fox 64
Final Fantasy VI (highlight: Dancing Mad themes)
Final Fantasy VII (highlight: Bombing Mission, Those Who Fight Further)
some tracks from Final Fantasy IIIj (boss battle theme), IV (Edward\'s theme, decisive battle, fiend battle, final battle, Cecil, Rydia), and V (Exdeath, Exdeath battle)
some stage tracks from Mighty Morphin\' Power Rangers
Chrono Trigger (Frog, Magus, Marle, Legendary Enemies, Zeal, Silent Light, 1000 AD town theme)
Puzzle Bobble/Bust-a-Move
Super Mario World 2: Yoshi\'s Island
Super Mario World 3: Super Mario RPG
Tail Gator
Pokemon GSC (Gold/Silver/Crystal)
Pokemon TCG (Trading Card Game)
some tracks from Pokemon RBY (Red/Blue/Yellow)
I know that a number of Final Fantasy tracks have been \"transcribed\" (the more accurate term would be \"rewritten and simplified\") for the piano, and are available as sheet music. I personally am working on my own piano (non-simplified) transcriptions of a number of game music tracks.