BlackScreen is a cross platform application that makes your monitor look black, no desktop, icons, or even your cursor. It's a great way to prank your family, and friends. Go ahead, and give it a try, just don't get the crap beat out of you :)
Openmark will be a Open Source benchmark that will have 32/64 bit options for video rendering tests on X11 as well as HD speed, FSB, etc benchmarks. Also many tools like: temp monitor, speed control, etc.