This is actually a news story, but still an interesting fact for people adjusting shaders:
“A scientist at Rice University has created the darkest material known to man, a carpet of carbon nanotubes that reflects only 0.045 percent of all light shined upon it. That’s four times darker than the previously darkest known substance, and more than 100 times darker than the paint on a black Corvette.”
http://www.chron.com/disp/story.mpl/front/5451632.html
-jeremy