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Edit*
Here are some sky texture:
- http://best-photoshop-tutorials.blogspot.com/2009/01/free-cloud-and-sky-textures.html
- http://www.burningwell.org/gallery2/v/textures/skies/
- http://www.sharecg.com/v/7684/texture/High-resolution-sky-texture?division_id=6
This is some of the sky texture from L.U.R.K
- http://www.megaupload.com/?d=2KH2NJTE
Edit2*
Nice looking textures
- http://mayang.com/textures/Nature/html/Clouds/index.html
- http://lostandtaken.com/2008/10/20-epic-cloud-and-sky-textures.html