POV-Ray is a very good raytracer, it's free and available for all
operating systems, its scenes are written in a C-like languange that all programmers should love.
These are the (little) images I made, if you want the source code,
Oops... I found only one image... I made other images, but it seems they get lost...
I enjoyed playing with
Fractint, fractals can be very beautiful
and the program has a lot of options.
Some desktop's backgrounds, the first is a drawing i made with Gimp, the other one
a photo of my desktop.