This jQuery plugin allows you to quickly and easily add mapping to your website. It has been designed from the beginning to handle lots of markers, lots of layers, and custom marker icons. The plugin can also manage sidebars for you.
kmlshare is a google maps api based websitesoftware. Users can upload kml files to the site, which is parsed and placemarks are stored in database, making the content browsable and searchable. View demo at http://www.vansham.com/janaagraha/