If the light source was one single entity that could be inserted as a seperate, moveable object, I would say make the sky a seamless transitional sky. Make the sun rise and set in a time span of a few hours...that would be cool.
Oh well.
I like plasma's random sky idea. Or maybe make it change once every few hours to a different (but similar) look. Like, go from Sunny, to slightly cloudy, to heavy clouds, to super heavy clouds, add rain, then make the sky dark, or something...