There is currently two sets of skyboxes, one set made by Hipshot, which I have released in the past, and and the other set comes from various authors with a set of new skyboxes for you to use.
Here are some in-game screens of Hipshot's skyboxes:
Spoiler: Skybox 1: "Grimm Night"
Spoiler: Skybox 2: "Miramar"
Spoiler: Skybox 3: "Stormy Days"
Spoiler: Skybox 4: "Violent Days"
Spoiler: Skybox 5: "Interstellar"Download Hipshot's Set:
http://rapidshare.com/files/2553590830/hipshotskies.pk3
Download Skybox Set 2:
http://rapidshare.com/files/2701275233/hdskies.pk3
Last Updated: Wednesday, July 24 (2013)