By the time you get to the end of a project and everything is set to start the final render, you realize that something is missing: the background! This is the moment that you wish for some generic 3d models to place behind your own model, just to compose a nice background. If you don't have any model like this yet, here is a great opportunity to download a building model created with Blender and ready to be rendered with Cycles. The project was created by an artist called mellogustavo and is available at BlendSwap.
The license of this model is Creative Commons zero, which means that you can do whatever you want with the file. But, its always nice to give credit to the author.