Create a map with locations (markers), powered by Google Maps API and jQuery jmap.
The plugin creates a map (using Google Maps) witch can be populated by users with markers (for us it represents their LUG "Linux Users Group" location, name, web site, coordinator and geographical position.
We are using it for example to show everyone how many LUGs are in your country. :)
It can be also modified to suit your needs. For example it creates a GeoRSS webservice, once you update the database with markers, the GeoRSS will be updated live.