Sketchucation - Sketchucation is a 3D SketchUp Community for students, professionals, designers, and hobbyists.
CGTips - CGTips is a 3D Architectural Visualization learning platform for Architects or interior designers to build their skills in an interactive way.
TheSketchupEssentials - TheSketchupEssentials is a community to get SkethuUp tutorials and help from professionals.
Open3dModel - Open3dModel is a library of millions of 3D assets and models for 3D printing, virtual reality, augmented reality, computer graphics, scientific visualization, and more.
Arroway-textures.ch - Arroway-textures.ch is an online repository of high-quality digital textures and 3D assets that helps you add them to your own 3D-content libraries and projects.
3dxo.com - 3dxo.com is a great place for both professionals and hobbyists to find some really cool, free 3D models.