Haoda Focusing Screen Review
http://www.camerahacker.com/Tools/In...oda_Screen.jpg
Another option is the KatzEye. According to the guys at work it's better because it doesn't "black out" as readily. They have a shitload of cameras that they manufacture for as well.
http://www.katzeyeoptics.com/ccp51/m...ory/20d_sm.gif