The Geolocation plugin allows WordPress users to geotag their posts using the Edit Post page or any geo-enabled WordPress mobile applications such as WordPress for iPhone, WordPress for Android, or WordPress for BlackBerry.

Visitors see a short description of the address either before, after, or at a custom location within the post. Hovering over the address reveals a map that displays the post's exact location.

Original authors: frsh, mdawaffe, automattic.

http://wordpress.org/extend/plugins/geolocation/