I recently bought Ninja Gaiden Black, the upgraded/re-released version of last year's Xbox game.
When you get through a few levels, one of the first unlockables is a 5 minute video of Dead or Alive 4, which will be a launch title for the Xbox 360.
I initially was underwhelmed, mainly because I was expecting more from the character models (which honestly looked pretty similiar in detail to the Ninja Gaiden models on the Xbox), but then I looked at the backgrounds and the intricate details that go into each scene. I'll just say this, I'm really looking forward to the X360. It should be a great system.
For the person who's gonna ask "How did you play an Xbox 360 game on an Xbox?".... I didn't. It's a DVD video of the game, much like your $60 DVD player wasn't used to design Star Wars.