Encyclopoedia of World Problems and Human Potential. The Encyclopedia has identified over 12,000 persistent problems of importance to humanity.
Kennedy, Donald & Norman, Colin. (July 1, 2005). What Don't We Know? Science 309, 75-102. This special section of Science magazine discusses the 125 most important questions to date for the field of science. A forum, which includes the original articles, asked readers to comment and add their own questions. The forum can be found at www.sciencemag.org/sciext/eletters/125th
Quotes from the articles of "What Don't We Know?"
"Unsolved mysteries provide science with motivation and direction. Gaps in the road to scientific knowledge or not potholes to be avoided, but opportunities to be exploited."
"Thoroughly conscious ignorance is the prelude to every real advance in science." James Clerk Maxwell