I used SmithMicro's Poser to create 16 images for my first Kindle offering.
SmithMicro found out, and did a Poser User Story on how I used their software in conjunction with a number of other free or low cost programs to generate the final images.
You can see that story (as well as many many more Poser User profiles) here:
http://poser.smithmicro.com/stories/wralewis.html
You can see a sample image (too large for posting) here:
https://www.me.com/ro/ray_lewis/Gall...13120453740001
What programs are the rest of you using for illustrations and covers?