http://marekdenko.net
One of the people that have inspired me with his astonishing 3d work is Marek Denko. His ability to create dirty and grungy looking artwork is some of the best I've ever seen. Almost all the artwork he produces is photorealistic, and that is something I admire. The reason why I admire that is because he never takes the shortcut of portraying something modern with lack of details.
One of the things Marek seems to focus on is doing a lot research before he starts producing something. If you have made a concept picture for your scene the next step would be to look for a lot of reference images. One of the resources Marek uses is www.environment-textures.com, but he also takes pictures of his own that he uses in the production.
I found out that one of the ways to achieve this photorealism is to add a lot of junk the scenes that could use a lot of different pre made materials. The materials used must have a complete set of texture maps like diffuse, specular, reflection and bump or displacement to ensure they look realistic in all situations. Combining this with a well thought out scene and good lighting you have yourself a photorealistic environment.