Dude, Theme Park! At least the one i used to play, which was technically called MacTheme Park, was full of epic win. I could make the millions in that game, and then move to Greenland, where my park would completely and utterly fail. My favorite part about it was that if you got too far into the red you'd commit suicide in a cutscene.
Now that I see it it actually says Zoo tycoon got relatively poor reviews, and its not as good as the computer version, sad! Now I have to think of other games I could get for the DS besides just Pokemon, since all of the really good ones seem to have come out in 2005.