In December 2008 I participated in one of Jeremy Birn's Lighting Challenges which are found at cgsociety.org and open to all. Models are provided (this scene was modeled by Alvaro Luna Batista and Joel Anderson) and after lighting and texturing the scene, you upload it to the forum where Jeremy will critique your work. He has been a Lighting TD at Pixar Animation Studios since 2002, so his advice is of great value!
After each challenge he selects some of the entries to go on his personal site's gallery. Check out all the selected renders here. I hope to do more of his lighting challenges in the future, and for anyone else who is interested go to this forum to participate!