Here’s the current list of demos available and when they will expire thanks to DSFanboy.com:

Crosswords DS-Wordsearch Demo (available until 8/03/08)
Crosswords DS-Crosswords Demo
Brain Age 2 Demo
Brain Age Demo
Flash Focus Demo
Trauma Center: Under the Knife 2 (available until 8/03/08)
Contra 4 (available until 8/03/08)
PICTOIMAGE (available until 8/03/08)
Carnival Games (available until 8/03/08)