I've got a 2Gb Micro SD card that I use for trialling stuff out, and another 2Gb for the 'keepers' which currently includes:
Advance Wars
New Super Mario Bros.
Yoshi's Island
Castlevania: PoS
Sonic Rush
Picross DS
Brain Training
More Brain Training
42 Clubhouse Games
Nanostray
Mario Kart
Elite Beat Agents
Trauma Center
Worms Open Warfare 2
Tetris DS
Advance Wars
New Super Mario Bros.
Yoshi's Island
Castlevania: PoS
Sonic Rush
Picross DS
Brain Training
More Brain Training
42 Clubhouse Games
Nanostray
Mario Kart
Elite Beat Agents
Trauma Center
Worms Open Warfare 2
Tetris DS
