Accion's Center for Financial Inclusion provides publications and resources on the microfinance.
The Asian Development Bank has sponsored numerous studies. (Search on microfinance.)
Symbiotics offers specialized investment solutions that connect socially responsible investors, to micro-, small and medium enterprises and value chain development projects in low-income economies in Africa, Latin America, Eastern Europe and South-East and Central Asia. Their publications include the Symbiotics Microfinance Investment Vehicles Survey.
IDEAS: Economics and Finance Research, hosted by the University of Connecticut Department of Economics, is a large bibliographic database that is freely available over on the Internet.
The Inter-American Development Bank, contains research and analysis into the history of microfinance and how it's being used today for social good as well as performance.
The United Nations Capital Development Fund offers “last mile” finance models that unlock public and private resources, especially at the domestic level, to reduce poverty and support local economic development.
For most of the resources below, consider search terms such as: microfinanc* or microbank* or microcredit* or microsaving* or microloan* or microlend* or microinsur* or micro financ* or micro bank* or micro credit* or micro saving* or micro loan* or micro lend* or micro insur*, where the asterisk searches the root of the word.