At this point, my flight sim world has a horizon and a solid blue sky. Can you give me some ideas on how to implement a sky with clouds, gradient, stars, etc. Is a sky usually done with a texture map, or procedural textures? Thanks.

Soon I'll have the same problem but still I'm not at that point and I havent't thought about it, so I can't help you now.

Thanks, all 9's... I think.

Sure, most anything's better than a solid color ;-)

Check into Sky Domes and Sky Boxes:
Sky boxes have no noticable artifacts of the box shape if done right, btw.
If you're feeling ambitious you might look around for some paper with a name like "a physical daylight sky model" or something like that.
Btw as for procedural or not - you can get better results going non-procedural unless you get a really nice procedural system going.
If all you need is some nicer looking skies, try getting terragen, and creating a sky box:

Render an image with a 90' FOV in each of the primary direction (North South East West Up Down)
Apply the textures to the inside faces of a box, place the box around the camera. When setting up texturing, set it to CLAMP, or manually edit the texture so the edges match up.

More questions? google! or ask here (if you have specific ones for me or others)
Also, this type of question has been asked *many* times, search the past topics for sky/clouds stuff if you want to be informed.

Good luck!
-Michael g.

Check out the sky/atmosphere and clouds rendering sections at vterrain.org and the very informative Sky-rendering techniques thread here on GameDev.

One of the simplest methods involves perlin noise to generate procedural clouds. If you search for perlin noise clouds you should get some good links. If you want to go the skybox route, imo it's more a matter of getting some high quality environment textures. There have been several threads started here on this topic, so I would search for them to get your started.