Best DC games IMO:
Bakuretsu Muteki Bangaioh (Quirky Treasure action game)
Black/Matrix AD (SRPG, import)
Chu Chu Rocket (Brilliant puzzle/party game)
Culdcept II (Magic the Gathering meets Monopoly, import)
Grandia II (RPG, not nearly as good as Grandia but still fun)
Ikaruga (Treasure shooter. import)
Jet Set Radio (quirky 3D platformer)
Kita e White Illumination (if you're into the ren'ai sim stuff... this one's really cute, import)
Last Blade 2 (solid SNK 2d fighter)
Mars Matrix (unique shooter)
Metropolis Street Racer (unique racer, predecessor to PGR series)
Napple Tale (Lovely Action Pop RPG, import)
NBA 2k2 (Sega Sports, great defense game)
NFL 2k series (Sega Sports)
Record of Lodoss Wars (interesting dungeon crawler ARPG)
Rez (quirky rails shooter which blends vector graphics with trance music, import)
Sakura Taisen series (get 'em all on one system... ST3 in particular is the best DC game, "dramatic adventure", import)
Samba de Amigo/SdA 2000 (both games + maracas are awesome)
Sonic Adventure series (3D Sonic)
Space Channel 5 series (pt 2 in particular kicks major butt but pt 2 is import only)
Street Fighter III series (awesome capcom 2D fighter)
Tennis 2k2 or Virtua Tennis (neat-o tennis game)
Toy Commander (fun game featuring toy vehicles where you do everything from race to dogfight to solve puzzles)
Typing of the Dead (funnest typing game ever!)
And I'll let you know about Border Down, Psyvariar 2, and Shikigami no Shiro II if I ever get around to opening them.