Judging from the games you listed, I would say a great choice would be Final Fantasy Crystal Chronicles Echoes of Time and Ring of Fates since they're very similar to kingdom hearts but still different enough. Oh and Kingdom Hearts Re:Coded if you don't mind another kingdom hearts. I think it's one of the better kingdom hearts games because of it's variety in gameplay. Someone already said Contra 4, which is one of the hardest action games on the ds. If you want racing I guess the Sonic racing game or Diddy Kong Racing. Either of the The Legend of Zelda games would be a great choice too.