I reccomend any or all of the following:
Animal Crossing: Wild World
Super Mario 64 DS (if you don't have Super Mario 64)
Mario and Luigi: Partners in Time
Save your money for: Tetris DS, maybe Metroid Prime: Hunters
All great games, and the ones about to come out are probably great games. It really depends on personal taste. Also I heard Age of Empires got a really good review, but I actually sort of doubt it was any good, since the review, I think, was in Nintendo Power.