Many of you have shown a lot of enthusiasm for Google Earth's ability to display 3D models. We can use this thread as a quick reference to the latest developments. Information will be updated as and when new developments happen.

Tools for modelling in Google Earth
SketchUp exporter	If you're a fan of SketchUp, try these plug-ins which will allow you to export your models to KML. Very basic right now, but improvements are on the way. Update! The SketchUp team have released an experimental plugin that will allow you to export your models to Google Earth. Download it here! Price: free. (SketchUp itself is available as a free trial, and is $495.00 to buy.
DProfiler™ suite	The guys over at DPEarth have created a couple of tools for you. DProfiler™ Modeler is a complete 3D modelling package which can export georeferenced objects to KML, while DProfiler™ Converter is a standalone utility that can convert 3D Studio and IGES models to KML. Price: DProfiler™ Modeler and DProfiler™ Converter are free to try, $399.00 and $149.00 (respectively) to buy.
Petrichor	Petrichor is a standalone converter for 3D Studio models. Support for other model file formats will be added soon. You are encouraged to provide feedback and offer suggestions for improvement. Price: free.