Google 3D Warehouse
Google 3D warehouse serves as a sharing platform for the sketch up users to publish and share your works. The 3D model has been categoried into 2 types: geo-referenced and non-geo-referenced. The geo-referenced is a real building object which has been built and located in Google Earth, and the non-geo-referenced is just the supporting 3D model like car, people, tree & etc....
There are some helpful modeling guideline (pdf format) for your better understand how to apply a new texture/material to the model (including the tutorial in Photoshop).