ArcGIS for AutoCAD is a free, downloadable plug-in application for AutoCAD that provides improved interoperability between AutoCAD and ArcGIS. Within the AutoCAD environment, you gain easy access to enterprise GIS maps hosted by ArcGIS Server.
Lexocad: easy to use and fast 3D CAD for painting, visualization and fun. - Fast: With part libary you are able to make anything in few seconds. - Powerful: Lexocad is simple, but you could do most complex models.
InnerSoft CAD is a plug-in for AutoCAD that install a set of productivity tools for Civil and Survey, Counting, Estimating, export to MS Excel, import from Excel, measurements in construction project budgets.
Point Cloud for AutoCAD is a plug-in for AutoCAD 2000, 2000i, 2002 and 2004. This plug-in gives AutoCAD to ability to process point clouds. You can import a point cloud into AutoCAD as it is or fit a surface that passes through the points.