Here is another mashup which puts both Google Maps and Yahoo Maps together.
When you scroll a map in one of the maps, the other map is also automatically updated. One thing you immediately notice is that the level of detail in each map is different. In some cases, Google Map seems to have more info, in few others Yahoo has the upper hand !
Why leave out MSN Local Map ? I guess soon there will be a mashup of these 3 services ? Or is there already one ?