Check out the Multitexture page on our wiki. http://wiki.polycount.com/wiki/MultiTexture Also modularity http://wiki.polycount.com/wiki/Modular_environments
Go to the game stores and sort by popularity. That will give you some ideas. We also have some resources here http://wiki.polycount.com/wiki/Freelance#Selling_Assets
We have some tutorials and examples here http://wiki.polycount.com/wiki/EnvironmentSculpting http://wiki.polycount.com/wiki/MultiTexture http://wiki.polycount.com/wiki/Terrain_in_The_Last_Of_Us https://polycount.com/discussion/159954/the-environment-art-of-halo-4/p1
I'll recommend the wiki, for moar relevant info: http://wiki.polycount.com/wiki/SkankerzeroModularCharacterSystem http://wiki.polycount.com/wiki/Character