This is a list of skies available in Source and GoldSource engine games, along with pictures of each skybox. The light_environment settings listed (Ideal Sun Angle, Ideal Brightness, etc) are suggestions based on settings used in official maps; other values may also be appropriate. To test skies in singleplayer without recompiling the map, bring up the console and enter sv_skyname . Quicksave the game, load it again and the old skybox should be temporarily replaced with the new one.
These skyboxes exist in the Half-Life: Source game files but are unused in game. They are available in Half-Life: Source, Half-Life Deathmatch: Source, and mods utilizing the Half-Life: Source content. Skies from Team Fortress Classic, Counter-Strike and Deathmatch Classic are present in the game files.
These skyboxes are available to Portal 2 and mods utilizing its content.
These skies are HDR capable. Go to Map Properties and change "SkyBox Texture Name"
to whatever sky you want. An env_fog_controller is also recommended.
These skyboxes are available to The Beginner's Guide and mods utilizing its content. You can browse files freely (they aren't packed in a .vpk, Location: The Beginners Guide\beginnersguide\materials\skybox),
These skyboxes are available to The Ship and mods utilizing its content. These skies are essentially HDR capable but adding _hdr at the end of the name for those tagged will use textures build for this purpose.