Blender Sensei sells a neat plugin that makes it very easy to switch and test different environments.
The Drag & Drop Environments addon for Blender allows you to drag any image into Blender’s 3D View window instantly creating the environment for both Blender Render and Cycles modes. You can even see your environment when working in Cycles mode! For more information on installing and using this addon watch the videos in the above playlist!
The addon also includes a simple Library feature providing you with quick access to your environments, Blender files, images as well as other elements in your library.
Drag And Drop Environments sells for $14.99.
