Link - Mapdex.org
Like it or not ESRI is a major player in web mapping. One of the projects (www.mapdex.org) I have been involved with has indexed over 1650 ArcIMS servers, serving nearly 30,000 map services, containing over 400,000 GIS layers. There is so much more out there’
Jeremy Bartley wrote that in the comments of Google, ESRI and FUD (15th reply). Most of the GIS web server sites we’ve created with ESRI server software have been behind firewalls and not available to the public. You’d have to just assume that ESRI’s total market penetration is so much higher than even GIS professionals assume. Mapdex is a really interesting project and if you really want to see what kind of web based GIS is available on the Internet, this is the place to start (outside of the Geography Network). As many Google Earthers are discovering, the information is out there, finding it is the problem. Mapdex could be the best way do find them out.
Jeremy also has a weblog, Mapdex Blog, that many should bookmark to follow more of this Internet web mapping phenomenon.