I can't recall any songs right now, but at the moment...
all alan's ballad songhttp://stat.ameba.jp/blog/ucs/img/char/char2/038.gif(Japanese)

Ai Otsuka - Kyngio Hanabi
Ayumi Hamasaki - HEAVEN
Mika Nakashima - Yuki no Hana
alan - Kanashimi wa Yuki ni Nemuru

Ayumi Hamasaki - Heaven

Ayu - You were...

There's just something so magical about this song to me.

I'm sure it would be by ayu, but there are SO many that it's wayyyyy too difficult!

Dearest
SEASONS
HANABI
RAINBOW
JEWEL
Days

Preach it baby girl. Most flawless ballad to grace Japan. Your favorites wish they could outdo this gorgeous, majestic, flawless song.

Acid Black Cherry - Kimi ga Iru Kara

Ayaka - Mikazuki
Ayu - Who..., No Way To Say, Dearest, No More Words, Forgiveness, HANABI
Namie - CAN YOU CELEBRATE
SPEED - Alive, White Love

Actually, I forgot to mention Akina Nakamori's "Nanpasen". It's one of the most haunting ballads ever and possibly rival's "infection" for me.

for me, the Nr.1 is Ayu - Curtain Call...her vocals there are totally fantastic

One? Not possible. xD

Utada--
Sakura Drops, Final Distance, Be My Last, Dareka no Negai ga Kanau Koro, Eternally, Stay Gold, Prisoner Of Love, Hikari, Passion ~after the battle~

Ayu--
Memorial address, Together When..., JEWEL, Moments

AKB48 - Hoshi no Ondo, Ai no Moufu, First Love, Ano hi no Fuurin
May'n - Glorious Heart
Sheryl Nome starring May'n - Liebe~Maboroshi no Hikari
News - Ai Nante
Nana Mizuki - NAKED FEELS, Thermidor -Vingt-Sept-
Kana Nishino - Kimi ni Aitaku Naru Kara
Ayumi Hamasaki - End Roll, teddy bear, M, HANABI, HAPPY ENDING, November, BRILLANTE, Memorial Address
Hikaru Utada - Deep River, BLUE
Kumi Koda - walk, Anata Dake Ga
alan - Yume no Garden

Koda Kumi - Suki De, Suki De, Suki De / Moon Crying
Seiko Matsuda - Anata ni aitakute
BoA - Winter Love

Now, Mika's new ballad is one of my favourites

Mika Nakashima - Sekai Ga Owaru Nara

Tohoshinki - Love in the Ice, Bolero (This song is what sucked me into being their fan.), and Doushite Kimi wo Suki ni Natte Shimattandarou?
abingdon boys school - and I love..., Desert Rose, and Via Dolorosa
alan - BALLAD
Daichi Miura - Stay with me
KELUN - SIGNAL -Acoustic ver.-
L'Arc~en~Ciel - HOSHIZORA
MiChi - YOU
Micro - Wipe Out
Utada - Deep River

..... there's so many, I'm too lazy to look through my playlist.

^That's not a J-Pop ballad lol

Probably Ayu's Moments. It's just perfect.

I can't possibly just pick only one.

I really love Ayu's ballads but I can't write them all down, so this these are just a few that I like.

Ayumi Hamasaki

Moments :heart
Dearest
HAPPY ENDING
Memorial address (This is considered a ballad right? xD)

Koda Kumi

you
Yume no Uta
Unmei
Cinderella before midnight (even though this is a cover)

Namie Amuro

Baby Don't Cry
The Meaning of Us
Four Seasons

One? Impossible. But here's some that have "stuck with me through the years", so to say:

Ayumi Hamasaki (top 5)
SEASONS, Dearest, M, LOVE ~Destiny~, crossroad

KOKIA - I believe ~umi no soko kara~, Mou aisenai, Arigatou
YUI - TOKYO, fight (acoustic), Tomorrow's way, Why me, I can't say
Ai Otsuka - Planetarium, Daisuki Dayou, Friends, Kingyou Hanabi
BoA - Eien, Every Heart, Milestone, LOVE LETTER, Meri Kuri
Kana Nishino - If
Namie Amuro - Baby Don't Cry
Utada Hikaru - First Love, HEART STATION, Dareka no Negai ga Kanau Koro, Can't Wait 'Til Christmas

sorry guys but eiko shimamiya's uchuu no hana has got all of your guys' ballads beat lol