Copenhagen Consensus - 'Cost efficiency' of tackling world problems
http://www.copenhagenconsensus.com/Files/Filer/CC/Press/UK/copenhagen_consensus_result_FINAL.pdfThis came out in 2004, but provides an interesting approach to thinking about which world problems would be most cost-effective to solve.
Spoiler: AIDS is at the top of the list and climate change is at the bottom.