My wife really likes these, they are reasonable and they will sell the material or frames if you want to do some of the work yourself. Helped the sound of my system more than anything else I ever did.
http://www.readyacoustics.com/index.php?main_page=faq&fcPath=13
http://www.readyacoustics.com/index.php?main_page=faq&fcPath=13