Both Google and Yahoo launched their mapping APIs at the Where 2.0 conference yesterday. You can read more about Yahoo Maps Web Services here and the Google Maps API here. You can also read Yahoo Web services evangelist Jeffrey McManus explain why the Yahoo product is better here. The most obvious difference is that Yahoo enables you to fetch maps by street address whereas Google allows only latitude and longitude. Unfortunately neither of them seem to permit me to use their maps within an internal application we have at work, since that would constitute private commercial use.