If you're interested in making your own, here's a thread to one I designed. Performs very well and almost ridiculously easy to build if you're somewhere that sells US dimensioned lumber --
http://www.diyaudio.com/forums/construction-tips/269366-easy-diy-depot-sound-diffuser-panels-step-step.html
http://www.diyaudio.com/forums/construction-tips/269366-easy-diy-depot-sound-diffuser-panels-step-step.html