I declare you to be ignorant if you don't think the DS is going to do well.

But anyway, definitely get one. The games I would recommend are:

Mario Kart DS
Phoenix Wright: Ace Attorney
Animal Crossing: Wild World
Metroid Prime: Hunters
Super Mario 64 DS (if you don't plan on downloading it off the Wii)
New Super Mario Bros.
Brain Age
Tetris DS
Big Brain Academy

Some upcoming titles you may like:
Star Fox Command (Release on August 28)
Pokémon Diamond/Pearl (Release in 2007)
Elite Beat Agents (Release on November 6)
Mario Hoops 3 vs. 3 (Release on September 11)
Final Fantasy III (Release in November)
The Legend of Zelda: Phantom Hourglass
Phoenix Wright: Justice for All