Animal Crossing. If you like that sort of game, it fits what you want perfectly.
That's one that I was seriously considering. Are there any good RPGs out yet? (I'm way out of the gaming loop right now)
Mario and Luigi is pretty good I hear, but I didn't buy it because Paper Mario was a little to easy/simple for me and I heard it was similar. Castlevania DS is really good, but that has been discontinued so you would have to find it used. But, if you can find one, it is definitly worth your money.
There aren't any good traditional RPGs out yet. There is one called Magical Vacation (or something) that looks pretty awesome, and is supposed to come out soon.