Because of the lack of good free skybox textures, I made a bunch of skybox textures with terragen. Each skybox took about 8 hours to render. Use them without restrictions, but please don't claim them as your own.
I'll release more textures and a model/sample as time passes.
enjoy
skybox:
stats: (should be copied to your game for the best effect)
sunlight yangle: 300 degrees (where 0 is north, 90 is east)
sunlight xangle: 25 degrees (where 90 is straight down, 0 is horizon)
sunlight color: 255 240 192 (red green blue)