Every track in the Compatibility Tester. That saxophone can't be topped.
Visit a Mii who's burning up with anger. You get what's essentially a battle theme rather than the normal twinkly apartment music.
A different battle theme plays when the Mii expresses desire to try again to win the heart of another Mii. Bonus points for also being a Moment of Awesome.
Between the unmodified songs you can teach a Mii, the Ballad ("Maybe, Baby") seems to be the most well received, due to its lyrics not being as Narmy as the others and the animations just plain being adorable.
The music in the stores changes to something pretty awesome close to Christmas. It's unfortunate that it stops playing once January rolls around.
It's more of a case of "heartwarmingly adorable music," but the gentle lullaby music that plays when your Miis have a baby is absolutely wonderful. If you're waiting for input from someone else on the child of them and their favorite fictional character, at least you have this track to listen to. When the child grows up, a more modern version of this tune is heard, and it's just as wonderful as the birth scene.
When a Mii is given its all-time favorite food, snappy music will play as it breakdances. Giving a Mii its super all-time favorite food will cause it to make a ":O" face and blast into space, as epic adventure music plays.
The jingly music when a Mii is in love and wants to confess its feelings. A sadder version of this plays when it misses its former lover.
Intense, violin music when a Mii is ready to propose to its sweetheart, complete with a Heartbeat Soundtrack.
During the wedding scenes, epic orchestral music is heard, and it's so heartwarming.
While the music at Mii Homes is good, there is soft music consisting of horns and strings when the Miis are smiling at each other lovingly.
Gentle music when the Miis are thinking of having a baby.
When the Mii proposes to its sweetheart, romantic music plays when the sweetheart happily accepts and everyone starts clapping. In the apartment later on, this changes to a more "New Wave" style.
The song that plays during the Kid-o-matic montage as the adult Mii relives their childhood. Same goes for the Age-o-matic montage where the kid Mii experiences what it's like to be grown up.
The music played when the parents read a letter from a traveler may be tearjerking, but it's also heartwarming, too. Gets happier during the scene where the traveler stops home; the happy music in the background shows they missed their family so much that they decided to come home.