ronenbekerman.com is a source of learning on all aspects of 3d architectural visualization.
In the blog & forums you will find articles & tutorials about 3d modeling & rendering with software such as 3ds max, VRay, SketchUP, Maxwell Render, Fryrender, Photoshop and more. This site will fit beginner, intermediate and advanced CG artists.
Here are some direct links you should explore.
The CityLIFE Challenge is currently running and you are welcome to visit and join in for a shot at some of the $40,000+ prize pool ;)
And visit past challenges to at the main challenges site.