Tales of Symphonia would definitely be up there, but I haven't played enough of it to know for sure (although it's great so far). Some other games worth picking up:
Ikaruga
Zelda: Four Swords
Timesplitters 2
Mario Kart: DD
Donkey Konga
Luigi's Mansion
Rogue Leader
Soul Calibur II
Zelda: Collector's Edition