What a great idea, easy but brilliant!

I took an alternative approach to this – a map of mapping mashups. Check out http://imagine-it.org/mashplanet/ to see what I mean.
Many map mashups cover certain regions-- so this helps you find the ones relevant to you.

Also relevant to this is the ability to include KML files in your sitemap so Google will index that information. (Check Google Maps API blog)

Nice. This is exactly the sort of thing that CSE is perfect for. I love that Marker can add a new source with a bookmarklet click.