"The Other Promise", a remix of Roxas's Theme only heard in the Final Mix version of the game. The 2.5 version is, if anything, even sadder. It starts off slow and quiet, but builds to an absolutely gut-wrenching crescendo.
"Fate of the Unknown" plays during the extended secret ending in the Final Mix. "Sunset Horizons", the wonderfully ominous song that plays during the original secret ending serves as its precursor.
Running down the Ravine Trail to avenge a boulder-beaned Goofy to "Vim and Vigor" is also epic. When combined with the pairing-up with Final Fantasy characters, it becomes an all-around Crowning X of Awesome.
"Hazardous Highway", a rockin' piece of Gummi Ship music. The two levels that feature it were already reminiscent of Sonic games, but the music clinches it.
The Gummi Ship themes are all surprisingly peaceful or upbeat, and the levels are kind of goofy, really. Well... all of them but the Star Wars-ish last one, with dreadnoughts of doom blasting the hell out of you, and its epic theme called "Battleship Bravery".
You want a kickass battle theme? Try "The Encounter"! The best part is that it plays mostly during Disney villain boss fights, so you get a good background song for your Catharsis Factor.
" Dance to the Death" is another fun but tense theme which plays for certain bosses, and the Heartless invasion of Disney Castle.
"Sora's Theme". Sure, it sounds all light and airy, because Sora's so happy all the time, but underneath it you can hear this steady, driving beat. Not only does it remind you of a heart, but it also shows his sheer determination to find his friends and generally win. It sends shivers down the spine.
"Working Together". It has such a happy beat to be a battle song, instead making you feel like you want to dance. It is the battle music for real Twilight Town which is more upbeat than the battle music for digital Twilight Town, so it's perfect music to uplift your spirit after the emotional ending of Prolonged Prologue. It is also carried over to be the battle music for Mysterious Tower in Birth by Sleep.
"Sacred Moon", the hauntingly awesome theme for The World That Never Was. There's a reason why some keep running around The World That Never Was besides the plot (and seeing Organization XIII's HQ).
The KHII arrangement of "He's a Pirate", remixed from its original Pirates of the Caribbean form into a battle theme. For fans unsatisfied with the original arrangement, the 2.5arrangement is far more faithful to Hans Zimmer's original rendition, about ten times more epic, and was far and away the most universally popular track on 2.5's OST.
"The Home of Dragons", the theme of the Land of Dragons, is kickass. Special mention should go to the 2.5 ReMix version. Some people felt that the original was a bit too screechy because it tried to make the generic PS2 string sample sound Chinese to... mixed results. Their general reception was "this song would be great with real instruments, not so much with MIDI." Sure enough, with 2.5, the re-orchestrated song uses proper Chinese instruments and sounds like it was always meant to.
The main theme from the Pride Lands world. Makes you want to go on an adventure, doesn't it?
Final Mix and 2.5 ReMIX provided for Christmas Town what a lot of people felt it always should have had: a proper town theme, "What a Surprise?!" and battle theme, "Happy Holidays!"
The events of Beast's Castle close with a fittingly beautiful instrumental version of "Beauty and the Beast". Kinda makes one wish this sort of thing could have been done with original music from the films in some of the other Disney worlds.
Friends In My Heart the somber, sweet, and nostalgic track that plays during Sora, Donald, and Goofy leaving Twilight Town and when Sora and Riku are reunited. The song is sure to bring a tear to the eye. That part of its melody is similar to "Dearly Beloved" only adds to it.
Sinister Sundown, Roxas' battle theme in Twilight Town, starts out fun and bouncy, but starts to slowly gain more instruments, as if they're warning you that something isn't quite right...