1.) Warioware Touched (but that's not your cup o tea...)
2.) Yoshi Touch-and-Go (i might like this more than wario)
3.) Polarium (puzzler.. its kinda bland but i love a good mental exercise)
4.) Super Mario 64 DS
Those are all the games i own. If you're dying for portable gaming, I'd recommend any GBA game. The DS offers a perfect screen for GBA gaming.
Mario Kart might not be online (i imagine it will be, though). Basically, you'd have to be in range of a wireless router (starbucks offer hotspots, i believe) and i think Nintendo will take care of the rest.
basically: wait till E3. Nintendo will show us the DS' online setup there, along with the rest of the DS titles we should be anticipating, such as Kirby: Canvas Curse, Meteos, Mario Kart, Animal Crossing, etc.