City Engine is a professional level procedural city generator that works with geographic maps, photos and parameters to generate virtual cities. The software was acquired by ArcGIS, wich developed a very cool web viewer (using webGL, of course) to view virtual cities in real time 3D with geographical information layers. It's a cool viewer, but lacks the game-style navigation that we in VRML/X3D and other web 3d technologies are used to. Still... i wonder if City Engine can be used to generate a large procedural city that can be converted to VRML or incorporated in a VRML world? Cool idea, but the software is not open source and quite expensive. Still, it could be a great solution to create a large city world with a minimal effort. Check their 3D cities here: ArcGIS City Engine web viewer. Scenes take a while to load.
(and they left out the ponte dei suspiri from the venice model. unforgivable!)
Yes, it is an interesting alternative player in the line of automatic 3D generators.
Looking trough their site found an interesting tool: "Carta Geológica de Portugal"
http://www.arcgis.com/home/webmap/viewer.html?webmap=a5a37519b33c4203955d09343e932f6d
vcard
it's cool but a bit on the expensive side. $500 for the basic version. I must confess that about a year ago i've hunted high and low for a cracked version for test purposes, but without any luck... the concept of procedural generation of a large space (city or other) is fascinating. http://www.esri.com/software/cityengine/buy