PDF was just put up on Konamis site...

http://www.konami.com/downloads/misc/2009_10_19_DDRHP3_X2_TrackList.pdf

I'm not sure what the difficulties are or if there are any more unlocks at all, but these are the songs appearing in both games.

DDR X2

Licenses:
Closer / Ne-Yo
Daftpunk Is Playing at My House / LCD Soundsystem
Disturbia / Rihanna
Do You Know (The Ping Pong Song) / Enrique Iglesias
Dream On Dreamer / The Brand New Heavies
Ice Ice Baby/ Vanilla Ice
I Know You Want Me (Calle Ocho) / Pitbull
Just Dance / Lady Gaga Feat. Colby O’Donis
La Camisa Negra / Juanes
Let's Get It Started/ Black Eyed Peas
Pocketful Of Sunshine /Natasha Bedingfield
So What / P!nk
Viva La Vida / Coldplay
When I Grow Up / The Pussycat Dolls
You Got It (The Right Stuff) / New Kids On the Block


NEW Konami Originals:
A Brighter Day / NAOKI feat. Aleisha G
Crazy Control / D-Crew with VAL TIATIA
DYNAMITE RAVE / NAOKI
Freeze / nc ft. NRG Factory
Gotta Dance / NAOKI feat Aliesha G.
Heatstroke / TAG feat. Angie Lee
La libertad / Cheryl Horrocks
La receta / Carlos Coco Garcia
Love Again / NM feat. Mr. E.
KIMONO♥PRINCESS / jun
roppongiEVOLVED / TAG Underground
Sacred Oath / TЁЯRA
Shine / TOMOSUKE feat. Adreana
What Will Come Of Me / Black Rose Garden
Takin' It To The Sky / U1 feat. Tammy S. Hansen
THIS NIGHT / jun feat. Sonnet
You are a Star / NAOKI feat. Anna Kaelin

From Japanese Releases
A Geisha's Dream / NAOKI feat. SMiLE.dk
AM-3P ("CHAOS" SPECIAL) / KTz
Blue Rain / dj TAKA vs Ryu
B4U ("VOLTAGE SPECIAL") / NAOKI
BRILLIANT2U ("STREAM SPECIAL") / NAOKI
Chance & Dice / 日本少年
D2R ("FREEZE SPECIAL") / NAOKI
Dance Dance Revolution / DDR ALL STARS
DYNAMITE RAVE ("AIR SPECIAL")
DEAD END ("GROOVE RADAR SPECIAL")
Keep on movin' / NM
MARS WAR 3 / JET GIRL SPIN
MOONSTER / kobo uniting Marsha & D.
MY SUMMER LOVE(TOMMY'S SMILE MIX) / MITSU-O! with GEILA
Pluto the First / WHITE WALL
凛として咲く花のごとく / 虹色リトマス
TRUE LOVE (Clubstar's True Club Mix) / jun
Ubertreffen / TAKA respect for J.S.B.
零 -ZERO- / TЁЯRA

Revivals:
Baile Le Samba / Big Idea
HYSTERIA / NAOKI 190
L'amour et la Liberte / NAOKI Underground
La Bamba / LH MUSIC CREATION
La Senorita Virtual / 2MB
Let the beat hit em!(CLASSIC R&B STYLE) / Stone Bros.
Love is Orange / Orange Lounge
TIERRA BUENA / WILMA DE OLIVEIRA
un deux trois / SDMS




DDR Hottest Party 3

Licenses
Boogie Wonderland / Earth, Wind & Fire
Bonafied Lovin' / Chromeo
Closer / Ne-Yo
DAFT PUNK IS PLAYING AT MY HOUSE / LCD Soundsystem
Detroit Rock City / Kiss
Disturbia / Rihanna
Do You Know (The Ping Pong Song) / Enrique Iglesias
Dream On Dreamer / The Brand New Heavies
Enjoy The Silence / Depeche Mode
Feel Good Inc. / Gorillaz
Good Times / Chic
Hungry Like The Wolf / Duran Duran
I'm Coming Out / Diana Ross
La Camisa Negra / Juanes
I Know You Want Me (Calle Ocho) / Pitbull
ICE ICE BABY / VANILLA ICE
Just Dance / Lady GaGa
Let's Get It Started / Black Eyed Peas
One Step At A Time / Jordin Sparks
My Prerogative / Bobby Brown
Never Gonna Give You Up / Rick Astley
Pocketful Of Sunshine / Natasha Bedingfield
Pork And Beans / Weezer
Praise You / Fatboy Slim
So What / Pink
South Side / Moby
The Space Dance / Danny Tenaglia
Viva La Vida / Coldplay
When I Grow Up / Pussycat Dolls
You Got It (The Right Stuff) / New Kids on the Block

New KONAMI Originals
A Brighter Day / NAOKI feat. Aleisha G
Be With You (Still Miss You) - nc ft. Eddie Kay
Crazy Control / D-Crew with VAL TIATIA
DYNAMITE RAVE / NAOKI
Freeze / nc ft. NRG Factory
Gotta Dance / NAOKI feat Aliesha G.
Heatstroke / TAG feat. Angie Lee
La libertad / Cheryl Horrocks
La receta / Carlos Coco Garcia
Lesson3 by DJ / Dr. DDR
Love Again / NM feat. Mr. E.
KIMONO♥PRINCESS / jun
Now's the Time / Brenda
PARADISE / Lea Drop feat. McCall Clark
roppongiEVOLVED / TAG Underground
Sacred Oath / TЁЯRA
Shine / TOMOSUKE feat. Adreana
What Will Come Of Me / Black Rose Garden
Takin' It To The Sky / U1 feat. Tammy S. Hansen
THIS NIGHT / jun feat. Sonnet
You are a Star / NAOKI feat. Anna Kaelin

From Japanese Releases
Brilliant 2U - NAOKI
CELEBRATE NIGHT / NAOKI
Keep on movin' / NM
Pluto the First / WHITE WALL
TRUE LOVE (Clubstar's True Club Mix) / jun

From Previous release:
Lesson by DJ / U.T.D. & Friends
Lesson2 by DJ / MC DDR
HOTTEST PARTY /
HOTTEST PARTY 2 /





I myself I'm probably just going to wait until the PS3/360 versions come out, mainly because I want to see the DLC the game has to offer.