[GeoNetwork Opensource][1] and the [Esri Geoportal Server][2] are two open source and free technologies that can be used to build Catalog Services for spatial information, and are both a great start.

However, I think both could do with more work on usability.

For example, Catalog Services from the [Esri Geoportal Server][2] can be accessed from ArcGIS for Desktop to discover OGC WMS services.  There is also an open source [CSW Client][3] to have ArcGIS for Desktop bind to and display those WMS services that has been shown to work at https://gis.stackexchange.com/questions/77567/is-there-public-ogc-catalog-service-csw-available-which-lets-arcgis-for-deskto.

On top of technological issues there are of course administrative issues around who can afford to create and maintain a comprehensive catalog of OGC and other GIS web services.  I suspect such a Catalog will need to be a federation of catalogs rather than a centalised monolith.

As an aside, I posted an [ArcGIS Idea][4] recently to encourage Esri to [Publish public test URLs for each OGC web service supported by ArcGIS][4] but it is yet to take off.


  [1]: http://geonetwork-opensource.org/
  [2]: http://www.esri.com/software/arcgis/geoportal
  [3]: https://github.com/Esri/geoportal-server/wiki/Geoportal-CSW-Clients
  [4]: http://ideas.arcgis.com/ideaView?id=087E00000004JalIAE