There are a few solutions. Ajax has some free Material settings which are fantastic. He has materials for the background that produce great skies. Metaform and Particles2 can both be used to make smoke and clouds, plus many other effects. These python script products can make the organic shapes inside of Poser5. Maybe playing with primitive props and applying the right material settings could work. There are many free material files from Mapps, Ajax, and RDNA. Many can be found here at Renderosity Freestuff.