Here are an list of exclusive games you can only find on the XBox at this current moment (the list of future games will be written later)

Air Force Delta Storm
Halo
Oddworld: Munch's Oddysee
NFL Fever 2002
NFL Fever 2003
Silent Hill 2: Restless Dreams
New Legends
Genma Onimusha
Buffy The Vampire Slayer
Bloodwake
Sega GT 2002
Rallisport Challenge
Dead to Rights
Prisoner of War
GunMetal
Dead or Alive 3
Elder Scrolls 3: Morrowind
World Series Baseball
Circus Maximus: Chariot Wars
Amped: Freestyle Snowboarding
All the ESPN Series from Konami (like 8)
MotoGP
NBA Inside Drive 2002
Outlaw Golf
NHL Hitz 2002
WWF Raw
Project Gotham Racing
4x4 Evolution 2
Azurik: Rise of Perathia
Artic Thunder
Cel Damage
Hunter: The Reckoning (for the time being)
Fuzion Frenzy
GunValkryie
Jet Set Radio Future
Nightcaster
Wreckless
Obi-Wan
UFC: Tapout

Some I may have missed or may have added accidently