I really wouldn't recommend the dictionary. Really, 5 Euros for that? I deleted it. And I bought it, I didn't get it for free...

I personally would recommend all 7 Art Style series games (PiCOPiCT, NEMREM, CODE, KuBos, BOXLIFE, AQUITE & INTERSECT), Link 'n' Launch, Aura-Aura Climber, Reflect Missile, 3D Space Tank, Starship Patrol, Trailblaze, and finally: Primrose.

For me, this are the best and most important DSiWare games.