The North American Mission Board is one of the most familiar missions organizations to me. They are Southern Baptist missionaries in the United States, Canada, and their territories. They plant churches and work with local associations (groups of churches within a region). They work in rural areas and inner cities. Here's a 3 minute video highlighting one NAMB missionary, just to give you some idea of what they do.
Today's prayer request can be found here: http://www.namb.net/prayerrequests/