The free Dystopia City Blocks come with a nice skydome with blue, cloudy, and night options: http://www.daz3d.com/dystopia-city-blocks-001-010-poser http://www.daz3d.com/dystopia-city-blocks-011-020-poser (edit: ah, mjc1016 beat me to it! )
Millennium Environment is ancient but still gets used quite a bit, I think, and it has a skydome too: http://www.daz3d.com/millennium-environment
I have WorldBase Lushlands too, but I haven’t used it much yet. It does seem like a great product. I don’t have Cloud Nine (yet) but I’ve heard many recommend it, so you probably can’t go wrong with that either.