You should buy the North American Navigon, there's a west coast one for $25 but I think you're better off buying the NA Navigon. I tried the tomtom but it doesn't let you know when to turn soon enough (often miss turns) But the Navigon has a map and shows you in advance when your gonna turn.
It's really annoying for apple to advertise iphone having a GPS....they do but it's just basically like mapquest or your maps app and does not talk etc.