I recommend
House of the Dead,
Virtua Cop 2,
Shen Mue,
Power Stone for utter Multiplayer Madness,
Soul Calibur is an excellent fighter (the story mode is awesome - ever fought an enemy in quicksand? Or balancing on a narrow girder? You'll get your chance here!)
Resident Evil Code: Veronica
Legcy of Kain: Soul Reaver in case you haven't played it on PSX
Metropolis Street Racer (Kudos!)
Rez (crazy meditative music-shooter that had a vibrating "toy" as extra available - google for usage reports^^)
Seaman (Microphone Controlled Talking Virtual Life Madness)
Shadowman (good game, even better atmosphere)
Toy Commander (Cool Multiplayer also)
The Typing of the Dead - Kill Zombies with your original Dreamcast Keyboard! If you happen to have one, that is
Zombie Revenge, Beat em Up with Tamagotchi-like VMU Minigame
Worms Armageddon - the classic
Headhunter - pretty cool 3rd person stealth action, nice motorcycle riding between missions
DC FTW.