Just a couple skybox textures I've made for my maps: 
[attachthumb=1]
For a ruined temple situated on a mountain middle of a desert. I think the clouds turned out pretty good. 
 [attachthumb=2]
A castle on a snowy mountains. Clouds could use some work on both of these. 
 
 This map isn't made by me (made by this guy 
http://gazoid.com) . I just used it to test the sky texture. One of my first Terragen2 creations actually. The billowy clouds need some depth. 
Crits&comments on any of these are most welcome.