Originally Posted by BestXXXPorn

Reaction games:
Tilt to Live
Fruit Ninja

Defense:
Dungeon Defenders
Defender Chronicles
geoDefense
GD Swarm
Fieldrunners (old but great)

Puzzle Games:
Cut the Rope (think they're on the Indie side)
Trainyard
Trism

Climbing:
TreesofDoom
DoodleJump


That should be enough to get ya started :P I know some of those were developed for Android as well.

EDIT: All of those games can be purchased for a sum total of less than one DS title :P