Final Fantasy IV
Yeah, I know. Some of these tracks are imaginatively named, eh?
If I were paying much attention to historical significance of musical pieces, this would be rated much higher, I reckon. But I'm not; I'm mostly just rating them by how much I like them, and honestly there's not much separating #44 from, say, #24.
This was THE boss battle music that set the bar for boss battle music. That bar remains where Final Fantasy IV set it today, pretty much. In fact, this is the only "standard" boss battle music to make this Top 50, though several "this is BIG" boss battle pieces are going to be seen here (including Final Fantasy IV's.)
The bottom line is, I'm not sure if, on the whole, Final Fantasy IV's slate of battle music has ever been matched. It's been 20 years now since that game blazed the path for the great RPGs of the 1990s, and I do believe that with each passing RPG that came along, battles were emphasized less and less, story more and more, until we got to Final Fantasy VII, which was the tipping point. Brought to you by the power of CDs, Final Fantasy VII introduced FMV, Full Motion Video, to the gaming world. There wasn't actually all that much FMV in the game--not much more than Zelda: Ocarina of Time for the N64, only a year newer and on inferior technology, offered--but it was very well received and that opened the floodgates. Since Final Fantasy VIII, the series has been less and less battling and more and more watching a movie with every installment, at least until it turned MMORPG.
But Final Fantasy IV, in addition to having one of the best stories of any video game even to this day, was very battle focused. By which I mean, if you wanted to get anywhere with the game (short of tweaking some very advanced stuff), you had to grind. And grind. And grind. The only way to beat the bosses was to gain more levels. And the challenge factor, by which I mean the grind more levels factor, was tuned down, a lot, from the original for the American version.
Of all the RPGs I played over and over from that era, the only one that required you to spend more time grinding levels was Lufia. And I'll be honest: Lufia had a great story, and that's why I stubbornly kept to it, but the gameplay was god-awful. That game still holds the all-time record for tedium.
Anyway, as I recall this was supposed to be about music. No piece of standard battle music was considered for this list; sorry, but I just listened to it all too damned much. But Final Fantasy IV probably also sets the enduring standard for regular battle music. (Well, EarthBound does, actually, but no one EarthBound track individually stands up to the standard music you heard in every battle in the Square games.) And this is the best normal boss battle music. And Battle With Golbeze's Four Emperors (or Fiends, or Gods, or whatever) ranks near the top of the super-boss battle music list.
Bottom line: Battling in Final Fantasy IV was a LOT more tolerable than in Lufia, and I suspect the music is a big reason why.
While we're here: In terms of battle system design, Square peaked with Final Fantasy V (the least known of the Super Nintendo series, as it wasn't released in North America until like three years ago.) IV's battle system was pretty good but tedious, and VI's was excellent except some options were pretty broken and over-centralized the game. VII's battle system was, honestly, poorly designed, and wasted ridiculous amounts of the player's time. Final Fantasy VII did not require much grinding at all, but mundane random encounter battles were aggravatingly long, causing you to spend about as much time in-battle as you did in Lufia. I keep a book handy to read while waiting for battles to end. That game REALLY needed an "animations off" button, like Ogre Battle had.
Or, Final Fantasy IV's battle music. If it had that, I might not mind so much.