As much as I like Eyes on Me, there's just so many good vocal themes. Here's all the main themes.
Final Fantasy VIII - Eyes on Me
https://www.youtube.com/watch?v=4qcW0oiLKHg
Final Fantasy IX - Melodies of Life
https://www.youtube.com/watch?v=94PdrQF1Ugs
Final Fantasy X - Suteki Da Ne
https://www.youtube.com/watch?v=3gm3p7jq4fs
Final Fantasy X-2 - Real Emotion (Opening theme)
https://www.youtube.com/watch?v=yfM-gStMwlE
Final Fantasy X-2 - 1000 Words
https://www.youtube.com/watch?v=ggjIDjAQtrw
Final Fantasy XI - Distant Worlds
https://www.youtube.com/watch?v=uGisUX1WqrM
Final Fantasy XI - Forever Today (Seekers of Adoulin)
https://www.youtube.com/watch?v=juL4t_ywo5w
Final Fantasy XI - Rhapsodies of Vana'diel (Chorus is actual players who sent in voice recordings. I'm in it as Mutekimaru from Asura. It's cool that I'm technically in the credits of a mainline FF game.)
https://www.youtube.com/watch?v=pVZgBk7_jTM
Final Fantasy XII - Kiss Me Goodbye (Purged from youtube completely apparently. Only covers and live recordings. First is just a FFXII ending video. Spoilers and Penelo talking over it. Second is a live recording.)
https://youtu.be/uoJS-13k_3s?t=509
https://youtu.be/gEGI0graDJ4?t=13
Final Fantasy XIII - Kimi ga Iru Kara
https://www.youtube.com/watch?v=3n_dq_YDCo0
Final Fantasy XIII-2 - New World
https://www.youtube.com/watch?v=P1vd0z3SLYo
Final Fantasy XIV - Answers (Winner lol)
https://www.youtube.com/watch?v=b96rrbo-_Ik
Final Fantasy XIV - Dragonsong
https://www.youtube.com/watch?v=FtuwltmTp9I
Final Fantasy XIV - Revolutions
https://www.youtube.com/watch?v=UmQm76wFfKk
Final Fantasy XV - Somnus (Plays in staff roll from main menu)
https://www.youtube.com/watch?v=-KKMbHNja_0
Final Fantasy XV - Prelude (Same as Somnus)
https://www.youtube.com/watch?v=7oSuk4EVLvI
Final Fantasy XV - Florence + The Machine songs (Stand By Me, Too Much is Never Enough, which plays in the main menu staff roll, and I Will Be, which isn't in the game yet lol)
https://www.youtube.com/watch?v=vv2DSmy3Tro
https://www.youtube.com/watch?v=bD6sTDH9Zdc
https://www.youtube.com/watch?v=vhGz6BLywIo
Final Fantasy Crystal Chronicles - Moonless Starry Night
https://www.youtube.com/watch?v=YFaJlBxqTOg
Crisis Core: Final Fantasy VII - Why
https://www.youtube.com/watch?v=M_ipWtjyuIM
Dirge of Cerberus: Final Fantasy VII - Redemption (Have some Gackt)
https://www.youtube.com/watch?v=Py8tpabV4Fw
Final Fantasy Type-0 - Beginning of the End/What Becomes of Us (One of the best pieces in the entire series, vocal or not)
https://www.youtube.com/watch?v=RgBJwDLt6sQ
Final Fantasy Type-0 - Ace's theme
https://www.youtube.com/watch?v=wwEcmNtz8Ps
Final Fantasy Type-0 - Utakata (Secret ending)
https://www.youtube.com/watch?v=Rz7h4Vj4hM4
Final Fantasy Type-0 - My Diamond (Alternate/Joke ending.) [High pitched Japanese girls warning] There's an English version too but they can't even stay in tune lol.
https://www.youtube.com/watch?v=ITHBuhR-Jq4
World of Final Fantasy - Innocent^2 (Main Theme)
https://www.youtube.com/watch?v=njZ9TNDUfFc
World of Final Fantasy - World Parade (Ending theme, most adorable scene of all time)
https://www.youtube.com/watch?v=C0Oo-NBIaF0
Chocobo Racing - Treasure Chest of the Heart
https://www.youtube.com/watch?v=VWYnwViwT0M
Chocobo Dungeon - Door Crawl
https://www.youtube.com/watch?v=bjku9dJ-x_E
I THINK that's all of them. That took way longer than expected.
Edit: I forgot Dissidia
Massive Explosion
https://www.youtube.com/watch?v=EXNrVKwhP4Q