How do I make clouds?

[Phoroneus]

I use cgtextures.com for skyboxes. My free account lets me use whatever images I want at a limited size, which is often more than enough for a skybox. In a worst-case scenario I do some editing in GIMP and make it passable.

If you're looking for more mobile, in-game clouds, I'm not sure how I'd do that, but if you just want clouds as a part of the sky your best bet is to look here:
http://wiki.frictionalgames.com/hpl2/tut...tutorial_3