- Shenmue
- Phantasy Star Online V2
- Sonic Adventure
- Sonic Shuffle
- Rayman 2
- Soul Reaver
- Puyo Pop Fever (NTSC-j)
- Evolution 1 and 2
- Skies of Arcadia
- Dead or Alive 2
- Street Fighter Third Strike
- Blue Stinger
- Resident Evil CODE: Veronica
- Grandia II is another must own Dreamcast RPG. Still on of the best battle systems I've ever played.
- Rez: a fantastic game if you can track it down
- Headhunter: a solid 3rd person action/adventure game
- If you enjoy rhythm games in the slightest, you'll definitely want to pick up Space Channel 5. Space Channel 5: Part 2 is even better, but really tough to track down, and coming out on PSN/XBLA soon. Samba De Amigo is fantastic, but be sure to make the investment with the maracas
- The Typing of the Dead is a really good game. Make sure to pick up a keyboard or two. (They're usually pretty cheap)
- Chu Chu Rocket is a really good multiplayer title.
- If you like fighting games at all, there are tons of great choices: Marvel vs. Capcom 2, Street Fighter III: 3rd Strike, Power Stone/Power Stone 2, Fatal Fury: Mark of the Wolves, Guilty Gear X, Dead or Alive 2, Soul Calibur, Virtua Fighter 3tb, Vampire Chronicle, etc...
- Crazy Taxi and Crazy Taxi 2
- Seaman is a very unique experience
- Confidential Mission is a really fun light-gun shooter
That's probably a pretty good staring point. Also, I'm right there with Pao and Sharky. Jet Set Radio is a must.