Three Skyboxes I made for various maps of mine.
Altitude: Skybox I made for my map IronAngel, it is meant to be bright, and with proper use of fog it hides distant objects very well.
Space 1 and 2: Meant for a space styled map of course, and gives you something to look at in all directions.
These skyboxes are free to all, and you can modify them to your needs so long as I get credit for the originals.
Use by either typing "/skybox jwin/X" in your console or adding the line "skybox jwin/X" to you map.cfg, without the quotes of course.
( replace X with alt, sp, or sp2 )
Cheers! Jake