This blend provides a convincing animated sky with wispy clouds. A few highlights:
- Drivers are used to make the built-in sky texture follow a sun lamp.
- The world texture is modified to make the sun directly visible in the sky (since Cycles doesn't show it by default)
- The clouds are on a large plane instead of in the world shader. This enables them to be lit by the environment (including the sun), and to cast shadows.
- For the clouds, I created a custom "Omni Shader" that scatters light in any direction without bias. At first I thought a 50% mix of the Diffuse and Translucent shaders would accomplish this, but that combination is biased against scattering perpendicular to the surface, and the result shows up as an ugly artifact.
Edit: I noticed that a couple people have removed their "Like" from this blend. I'm still learning, so if this sky doesn't work well for you, please leave a comment explaining the issue.