A site by DM Solutions groups with various web mapping frameworks that sit on top of MapServer and other Open Source GIS technologies.

Check out their Ka-Map API which utilizes AJAX technology and PHP Mapscript to provide an interface very similar to Google Maps.

Also checkout MS4W which is a full webgis ready-to-install solution for MS Windows which comes packaged with a self-standing apache webserver, PHP 5, Mapserver and Mapscript, and FWTools. Note you can use portions of it if you don't want the full package - e.g. the Csharp mapscript files in IIS and the mapscript CGI in IIS.