Contenders for mashup dominion
The web site Placeopedia is a mashup using Google Maps, connecting cities with their Wikipedia entries. In other words, it’s sort of a geographical version of Wikipedia for the planet Earth. It’s still in a very early phase and there are lot of contenders, but it could be interesting to watch it grow.
If you prefer to tag areas instead of points, WikiMapia is an alternative. It allows users to tag map areas and write their own comments.
Of course, there is a Virtual Earth counterpart. It is called Map Cruncher and released by Microsoft.