"Emancipation" is quite calming, but when the bell strikes, it invokes a feeling of uncertainty. In later part (about 3:18), it turns into an awesome rousing theme.
"Whiskey Corridor" cannot go by without a mention, especially not with what starts at 2:50.
"Stonehenge Attack". Made doubly terrifying when you hurry to obey the sudden order to drop altitude, not knowing why it was given, and watch as half your allies get blasted out of the sky above you.
Breaking Arrows and Breaking Arrows 2. The tension instilled by the music as you race against the missiles will give you the chills. Especially the last (nuclear) one.
Mobius. Get your plane, listen to the base commander give a Rousing Speech, and go destroy the Megalith.
Ace Combat 5: The Unsung War
"Hrimfaxi". A reprise of the music from the earlier Scinfaxi fight, but with some insane electric guitar thrown in for effect.
"Supercircus". Absolutely perfect for the scene it's pulled on: in the middle of safe territory, the four of you suddenly get Zerg Rushed by 20-30 Yuktobanian fighters and what was supposed to be a simple ceremonial flight quickly devolves into a nerve-wracking dogfight for your lives while waiting for reinforcements that turn back and jam the airwaves once halfway there.
"15 Years Ago". Another piano version that you normally hear during Nagase's and Gennette's musings on the Belkan war, but also plays during the final mission if you beat the enemy planes quick enough. This song, along with the ordinarily sappy dialogue, makes those two minutes leading up the SOLG assault practically into a CMOH/Tear Jerker.
"Unsung Heroes". A short, yet still magnificent piece, truly befitting your final victory.
"Glacial Skies". That crescendo though. You can practically feel the icy wind on your face, as there's not a warm instrument to be heard, all shimmering violins, cymbals, and castanets, and even the guitar is razor-thin. Gorgeous.
"The Valley Of Kings" perfectly portrays the feeling that you're going to the enemy base to finish them off once and for all... somehow.
"Avalon". The enemy is preparing to launch nuclear missiles, you have limited time to stop the launch AND you have to fly throught a tunnel to stop it. The first part of the song catches the tension of the moment, but the second part gives a heroic feeling.
"Zero". This is perhaps Keiki Kobayashi's magnum opus.
Even two "unknown" tracks that don't have a title are good. The first one plays during second part of missions "Ice Bound" and Wild Card", while the second one plays only during the raid on Sachana Air Base in "Blitz" and includes a portion of the game's main theme.
"Malebolge". Fitting for the fight against Pasternak in the CF-44 Nosferatu.
"San Loma Assault" at first seems run of the mill for Ace Combat, until the brass comes in.
If you'd already played AC 4 and 5, you probably knew something bad was going to happen the moment they told you your last mission was a peaceful patrol over Gracemeria. When "City Lights" starts playing, those suspicions are confirmed.
"Gravity". The Ending Theme with some pretty awesome lyrics. note The 3D Cross Rumble soundtrack calls this song "Like a Phoenix Rising," but in the credits for Assault Horizon Legacy this song is titled "Gravity." This is also the name Noel herself used for the song.
"Fighter's Honor". It's been an established tradition for Ace Combat protagonists to get an awesome orchestral song singing their praises for the final battle, and now Scarface One gets his own.
"Stonehenge Remix" Played during the Entirety of Mission 4, and has also been used during all the Multiplayer runs against Stonehenge and the Second and Third Multiplayer runs against Moby Dick/Agaion.