What games have you completed on your DS? The definition of "complete" is up to you, whether or not you have completed every side quest and bonus. I tend to call a game complete when I've finished the storyline.
Games I've completed on my DS:
The Legend of Zelda: The Phantom Hourglass
The Legend of Zelda: The Minish Cap
Super Princess Peach
Professor Layton and the Curious Village
Mystery Case Files: Millionheir
and I think I've unlocked everything in Brain Age 2. I still need to unlock everything in MarioKart, and the next game I'm starting on is Golden Sun for GBA.