Cloud Maps
You can overlay cloud maps onto the rendering of the earth using the cloud_map option in the configuration file.
A high resolution (8192x4096 pixel) static cloud map can be found at the Visible Earth site.
Xeric Design provides near-realtime cloud maps that can be used with Xplanet. Subscriptions may be purchased here for hourly cloud maps up to 8192x4096 pixel resolution.
You can also use lower-resolution cloud maps from the Space Science and Engineering Center at the University of Wisconsin. Their Global Satellite Composites are updated every three hours. Use the cloud_ssec option in the configuration file for versions later than 1.0, or the -cloud_ssec option for versions before 1.0.