3d architectural rendering is not possible without a good 3d model; I’ve compiled a small list of site that offers free download of 3d models and AutoCAD human library.
3Dmax 3D Model Library
If you happened to be in the 3D modeling and rendering industry, you ought to check out this website where they provide a tidy collections of 3Dmax and AutoCAD 3D models library, all for free.
Google SketchUp 3D Library
For Google SketchUp user, they have the SketchUp warehouse where everyone submits their 3D model to build the biggest open source 3D library in the world. Unlike 3D max where most of the 3Ds comes with a price tag, Google SketchUp Warehouse offers a wide range of 3D models all for free!
Search DWG and DWF files online
Alternatively, you can try this DWG search engine, it claims to be able to locate most CAD files available online.
AutoCAD People and Human CAD .dwg Library