Nearby.org.uk has a page of useful utilities for both Google Earth and Google Maps. Many are UK-oriented, but others have more general utility:
- A network KMZ link that plots a UTM grid in Google Earth
- A similar link for the Military Grid Reference System (MGRS)
- A web-based utility for sorting placemarks in a KML file by name; very handy if you have a long list of unsorted placemarks
- Another web-based utility that takes a KML placemarks file and groups them by country/state/county
… and more. The whole site is worth poking around, especially if you’re from the UK.