Operation World is an alphabetical index of all the countries in the world. It includes basic facts about each country such as their population, type of government etc as well as answers to prayer and challenges to prayer. This has helped me become more informed about approximately how many followers of Jesus there are in each nation and where prayer is needed the most.
Duncan and I have the old 2001 print edition which looks like this:
But there is now an updated 2010 version:
Or you can visit the website.
Use these to uphold Christians around the world in prayer.