I don't know if you read any of my post or not. Because I have posted this link before. You might just not have seen it. I went back to http://renderosity.com
and found a whole bunch of sky backgrounds and standalone programs there listed you can download for free. You just signup for free and go to free stuff and I mean there is a motherload of everything on their free listings. Just about any subject just do a search type in a word. I typed in sky and got 3 pages of listings.
I hope this can help. I went to the sites that had some of the free stuff listed. Here is a bryce download.http://www.awakenedeye.com/free.htmlhttp://www.apachedesign.com/download_cinema_sky1.htm
Here is some more sky stuff for bryce.http://www.dhtmlnirvana.com/graphics3d/http://hometown.aol.com/roch3d/index.htm
Anyway that gives you some sky backgrounds. There is alot more but you can do searchs on http://www.renderosity.com
and find what you need. You might trying search for clouds.
I mean sky is blue or some color but its the clouds that give it a sense of movement.
I did a search on space and found some great space ship corridors etc. Makes me want to do a space movie.
PS let me know what you think ... Just wanting to help still working on my movie with the winged character and its going pretty good hope to put something up soon.