In no particular order:
Sonic Adventure 2 Battle
Sonic Adventure DX (before you flame me, I never had a Dreamcast to play the supposedly superior original)
Wind Waker
Super Smash Bros. Melee
Tales of Symphonia
Metroid Prime
Pokemon Coliseum (what? I found it fun)
Paper Mario: The Thousand Year Door
Resident Evil 4 (unfortunately don't own it, but liked what I played)
Metal Gear Solid: Twin Snakes
Honorable mention goes to Skies of Arcadia, and it might have made the list if I actually played more than the first few hours.
Sonic Adventure 2 Battle
Sonic Adventure DX (before you flame me, I never had a Dreamcast to play the supposedly superior original)
Wind Waker
Super Smash Bros. Melee
Tales of Symphonia
Metroid Prime
Pokemon Coliseum (what? I found it fun)
Paper Mario: The Thousand Year Door
Resident Evil 4 (unfortunately don't own it, but liked what I played)
Metal Gear Solid: Twin Snakes
Honorable mention goes to Skies of Arcadia, and it might have made the list if I actually played more than the first few hours.