"Techno de Chocobo" sounds like "Technopolis" by Yellow Magic Orchestra.
The key, multiple chords and parts of the bassline are taken straight from Sakamoto's song in a really obvious manner, and even the instrumentation is similar, as both songs use a string section and an acoustic bass.
"Kids in the Street Corner" is essentially a more medieval-sounding version of the 60's hit "Sukiyaki" by Kyu Sakamoto.
"The Magic House", and the unused dungeon music from Final Fantasy II on which it's based, both sound just like Mozart's "Rondo Alla Turca".
The more rocky parts of the tune seem to have been inspired by Emerson, Lake & Palmer, "Tarkus" in particular.
"Dancing Mad" sounds quite a bit like Triumvirat's " The Burning Sword of Capua ".
"Terra" shares a bassline with the Mars Movement of Gustav Holst's The Planets.
Then there's "Slam Shuffle", or Nobuo Uematsu's take on The Pink Panther theme.
The intro to Celes's theme (before it transitions into a reprise of "Aria de Mezzo Carattere") bears no small resemblance to the file select/fairy fountain theme from The Legend of Zelda series.
The bassline sounds like it was ripped straight from Carl Perkins' "Honey Don't". Goode" but is more thematically similar to "Rock This Town" by the Stray Cats. Bad" is named after Chuck Berry's "Johnny B. Of course, it also sounds very similar to the theme from The Good, the Bad and the Ugly.
The first few bars of Shadow's theme sound a lot like the opening theme to The Virginian.
It also resembles Kraftwerk's Trans Europa Express.
The title theme sounds like " Thus Spake Zarathustra " played on an organ.
The beginning of Alkan's piece is very close to that theme apart from it being slower and for piano.
One that falls between this and orchestration: Terra's Theme from Final Fantasy VI and Alkan's La Chanson De La Folle Au Bord De La Mer which dates to 1847.
Locke's Theme and the theme of Back to the Future.