Aria of the Soul, a remix of the original Velvet Room theme. Dignified and mysterious, perfect for Igor, and so amazing that it's re-used in all Persona games afterwards. Then...
It's fair to say that nothing else in this game's OST will be stuck in your head more than BABYBABYBABYBABYBABY. The rest of "Mass Destruction," the game's main battle theme, is pretty iconic too. The version from FES adds even more jazz to the song, including a brief horn solo before the first "BABYBABYBABY..." and additional lyrics. It serves as a follow-up of sorts to the original version.
Once you get to the last month of the game, the themes for the locations around the city get changed. And the city theme, Memories of the City is the best one of them all. The more somber-sounding theme really fits the darker look of the city, as well as the sheer weight of what the characters are preparing to do.
Living with Determination often plays during sad moments and when someone reaches the resolution they need to evolve their persona. A remix plays after New Year's Eve in the dorm. It pumps the player up to prepare for the arrival of Nyx.
Master of Shadow, the theme of the Moon Shadow bosses. Otherworldly awesome.
Deep Breath Deep Breath, the song only plays during when you're on the train going to fight the first shadow. But it's still awesome.
Darkness, the theme for the final boss fight of The Answer. Sounds a bit like "Divine Identity" (see the Digital Devil Saga section), and evokes the same feeling: "Let's go kick ass!"
Brand New Days -The Beginning-, which is the main screen theme. It also is the theme of choice for one of the most heart-wrenching scenes in the game. A vocalized remix plays during the credits to The Answer.
School would be much more popular if they piped the upbeat and catchy Want to be Close into the halls. Oddly, take away the percussion and piano and you've got the appropriately titled Tranquility.
Mistic (sic), which is the basis for the themes of the different Tartarus floors and plays during one of the tensest moments in the game (when the player decides whether or not to kill Ryoji). It's based around a deep relaxing piano and string melody, but avoids Soundtrack Dissonance.
When The Moon's Reaching Out Stars, an incredibly catchy and upbeat town theme. To contrast with this song's fast-paced, almost techno feel, Persona 3 Portable adds the equally catchy and upbeat Way of Life for the female protagonist.
Sun, one of the new overworld themes added for the female protagonist in Portable. Whether you think it's So Bad, It's Good or just plain awesome, one thing's for sure: it'll never get out of your head.
The Spring of Birth movie brings us "More Than One Heart". Appropriate to the movie's title, the song makes you feel like you're out in the middle of a spring day, basking in the sunlight.
Fate is in Our Hands, the theme for the second movie, Midsummer Knight's Dream. Lotus Juice's flow is absolutely jaw-dropping, especially the section from around 3:20 to 3:50.