We already include a [http://www.geonames.org GeoNames] search box:
 * http://trac.geoext.org/wiki/ux/GeonamesSearch

This should be extended to allow access to other systems:
 * MGRS/UTM grid refs

[wiki:BluePrintGISGeolocator]
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[wiki:BluePrintGeographicInformationSystems GIS BluePrints]