Script Summary: Shows the map centre latitude/longitude coordinates in Google Maps.
Copyright: 2011-2013, James Inge (http://geo.inge.org.uk/)
License: MIT License; http://www.opensource.org/licenses/mit-license.php
Google Maps - Show Coords
Adds a widget marked "Show coords" in the sidebar next to the map. When you click on it, the label changes to show you the latitude and longitude of the point at the centre of the map window. The coordinates do not change as you drag the map, but update if you click again.
I use this to find locations to program into my GPS, or to feed into geographical search engines. If you are careful with your mouse, you can highlight the coordinates to cut and paste into another application.
The coordinates are shown in degrees and decimal minutes (DD MM.mmm) on the WGS84 datum, with north and east positive. There is a variable at the top of the script that you can edit to give you decimal degrees (DD.DDDDD). If you want decimal degrees, it might also be worth looking at Google Maps Labs, which currently has a couple of similar features.
** Update Jan 2013 to work with secure https access to Google Maps and improve cross-browser compatibility **