I agree that Kerkythea is probably the best free renderer these days as far as features and user friendliness....it also has a vibrant website and forum. Radium also looks impressive, but but not as many people on the forum.

My criteria for renderers is rather specific, I've been waiting to see if anyone can render diamonds with Kerkythea...it should do well with colored gemstones since it has caustics.

Here's the same model as before but with softer shadows done in Bryce. It took me a while to figure out I had to shut off "fog and haze" to get a rendering that wasn't so cloudy!

-jdk