Halo, Amped, Dead or Alive 3, Munch's Oddysee, NASCAR Heat, Project Gotham Racing, Max Payne, Silent Hill 2, Dead to Rights, RalliSport Challenge are all very good games and all support 480p As do most other Xbox games.

Tony Hawk Pro Skater 2X supports 720p and Madden 2002 supports 1080i (I would guess the new Madden 2003 would as well) according to NextGen magazine.

Btw, Halo is a killer app; it's sold 2 million copies worldwide and is a kick @ss game.