Pretty much everything said so far about Mother is spot on (kudos for using the NES version of it, I think it's the best one so far)
If I had to choose from Mother 3, it'd be almost impossible, though I really REALLY like "
Misplaced Revenge", "
Monkey's Delivery Service". But when it comes to complete badassery, nothing comes near "
Natural Killer Cyborg"... Hell, I'm making some real tough omissions.
To both Bigboi and BlueWarrior, while I do like "Nothing but Tangerines", I've always liked "Lorenzo's Soil/ISO 9001" song as a kid. I played the Genesis version and the song transmitted a sense of melancholy or immense sadness...
That is until I heard the Saturn version, which has a cool (albeit generic) guitar solo, and seems to end with an arrival to the pearly gates.
Moving on to another series, goddamn Phoenix Wright. These guys know what they are doing. And the Orchestrated versions are even MORE awesome.
Cornered! - Chronology
Objection!
Also, Chrono Cross' soundtrack is universally regarded as OH MY GOD YESSSS, so I won't delve into much more detail. (Also Scar's Time is horribly overrated (Don't get me wrong, I actually really like it, but I like other ingame songs better than that one))
EDIT:
How could I have forgotten this gem?
Also Katamari on the Rocks. (and that song with singing children)
But still, the best videogame soundtrack goes to "The Beatles: Rock Band". You just can't top Sgt. Pepper's.
You can't.