I am advising a PhD student who is working on NGOs' performance versus leadership traits. However, what you seek has to be researched since you have to define which impacts you are interested in. Maybe you may find information within the reports of the European Union or IMF which support NGOs work and performance because they provide funding.

Are you thinking in terms of cost-benefit analysis of NGO productivity? The journals below focus on benchmarking NGO results. I have also attached a funding criteria, from the government of Canada, to provide contextual expectations:

Chowdhury, T. A., & Mukhopadhaya, P. (2012). Limitations of the theories of nonprofits and benchmarking services delivery dimensions of poverty-reduction programs in rural Bangladesh. Journal of Nonprofit & Public Sector Marketing, 24(4), 325-350.

Hansen, E. G., & Spitzeck, H. (2011). Measuring the impacts of NGO partnerships: the corporate and societal benefits of community involvement. Corporate Governance: The international journal of business in society, 11(4), 415-426.

Malki, E. (2008). A benchmarking model for measuring the efficiency of a humanitarian aid program: a case study of an international NGO. Available at SSRN 1288206.

Schulte, Y. (2008). Benchmarking the process of democratization in Kyrgyzstan by defining the role and functions of NGOs. Social Research Centre, American University of Central Asia (Eds.) Kyrgyzstan Today. Policy Briefs on Civil Society, Migration, Islam, Corruption. Social Research Centre: Bishkek, 4-11.

Lindenberg, M. (2001). Are we at the cutting edge or the blunt edge?: Improving NGO organizational performance with private and public sector strategic management frameworks. Nonprofit management and leadership, 11(3), 247-270.

The first link, is for an organization that grants funds to NGOs, it may be useful to see how the application process is undertaken and how they monitor the funds once dispersed: 

http://www.fundsforngos.org/donor-agencies-2/

Here is a list of NGOs and contact info:

http://www.dainet.org/sdnp/list.asp

Yes, Impacts of NGOs can be measured by

1. Compare the changes taken place due to intervention with Baseline, if it is community based intervention.

2. NGOs inter -organizational relationship with other Government or NGOs

3. Physical infrastructure facilities developed in operation area vs before their work and after the situation in the areas

4. Sector-wise Stakeholders Organized by NGO

Likewise we can have a framework.

Best are - Before-After comparison; inter-organizational partnership of NGO

But most of the external evaluations do not cater to all these areas while doing the assessments. It is very costly and tricky to measure these results, with explicit recommendations.

Good Answer Daryn Dyer