I have created a set of archives that contain Q3A skyboxes collected from various WEB sites. Following is the 'readme' of the archive set:
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Disclaimer:
These skyboxes have not been produced by me, I take no credit whatsoever
for them. I have put them together in these archives for convenience and
made a few slight modifications / improvements.
This archive contains a lot of (actually 79) different skyboxes
collected from various WEB sites all around the world. This is the
result of my frustration as a mapper (due to the lack of good skyboxes
in the standard distros of Q3A, Openarena and Nexuiz).
As far as I could determine, these skyboxes are all free to use
non-commercially. Some of them may even be released under the GPL. You
have to check the individual 'readme' files included in the separate
skybox folders. If in doubt, connect the original author, provided that
the e-mail is still valid which is not very likely

Each skybox has a working Q3A shader script, these are stored in the folders
'0_scripts'. Some of these scripts were made by me because the corresponding
original works did not include any.
I have checked the sun's direction & elevation values in every single
skybox in the archive. I used a simple test map for this. The MAP file and
textures necessary to build this test map are in the archive Q3SKYINF.ZIP
(see below). I also included a text file containing instructions on how to
use the map.
The archive is split to several sub-archives because the full lot is
about 128 MB compressed. This would be too large for someone who wants to
download just one specific skybox. On the other hand, if each box would
be a separate archive the whole thing would be a PITA to manage. The archives
are named Q3SKY01.ZIP, Q3SKY02.ZIP, etc.
There is an additonal small archive called Q3SKYINF.ZIP, this contains a
galery of the available skyboxes (one representative image for each box)
as well as a table of the location of the boxes in the different archives.
It also contains the special test map I mentioned above. You should download
this archive first.
I hope that these packs are going to be useful for mappers all around. If
you have a nice skybox (made by you or downloaded) which is not yet in these
archives, just let me know and I will include it if you wish.
Enjoy!
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A couple of teasers




Right now the files are kept on my personal WEB page, but I will try to submit them to LvL for wider accessibility. Download locations:
http://menczel.extra.hu/q3sky.html
mod edit removed dead links