Here are two key resources from the Guttmacher Institute:
Unmet need for contraception: 2011 Guttmacher unmet need report,
The benefits of investing in contraception: addingitup-guttmacher-benefits of investing
And, here is data from the U.N. on worldwide contraceptive prevalence: 2011 UN prevalence wallchart_front
Note 2016: Link broken? Doing historical research? Try the previous (2011) archived version of our site if you need a particular link or reference.