Recently I worked a bit on the exporter for Radiance files. Traditionally my first test scenes came from the Radiance book. After that I was digging a bit through some models from the Radiance gallery site.
The current state of the Radiance exporter can't export textures (yet), but we can export the scene for Radiance and render it:
Other examples I recently converted to Radiance originally come from lighting challenges on the 3drender.com web site. Here some examples:
The original scene rendered by Cycles using some compositing looks like this:
You can download the Radiance files (and the same scene for other renderers) here.