The Human Development Foundation of North America (HDF) does not just focus on literacy. It's one of five cornerstones of the program, designed to fight poverty in Pakistan. There's a huge focus on community. One thing the HDF does is establish and maintain schools, including adult literacy classes. Close to 5,000 adults have been reached by their efforts. There are many ways to get involved. In addition to standard donations, you can sponsor a family for $15/month. At trade paperback prices, that's giving up less than two books per month.
The HDF has a four-star rating from Charity Navigator.