Google Earth Overlay
(Needs more work)
You can download the plug-in for Google Earth that allows you to display all the caches registered in OC UK. Google Earth can be downloaded from http://earth.google.com/
* Caches for OC UK can be downloaded from the address http://www.opencaching.org.uk/util/google-earth/opencaching.kml
Save the downloaded file to disk and open it in Google Earth. On the map you'll have a list of UK Opencaches and you can click on an icon to see the details of a cache.