There's really too many to name off-hand. Some of the less mainstream titles but excellent titles that come to include Space Channel 5, Rez, Samba de Amigo (and the 2000 "sequel"), Chu Chu Rocket, and Bangai-O, to name a few. It's still a valid system for me now, despite ports, as a lot of my favorite DC games still remain on the system, and it's the more economical choice for certain games, mainly 2D fighters.
Sonic Shuffle was okay, but hardly one of its best games.