Free, high quality, 3d rendering program?

Can anyone recommend or does anyone know of any high quality 3d rendering programs that are easy to use and free to download?? Im not amazing at 3d stuff but have used microstation, rhino and sketchup in the past…but am never overly pleased with the renders you get from them. Ideally i would like to be able model some simple objects in sketchup and then import them into something else to get a realistic texture/lighting effect.