This organization developed a national program evaluation study. There is a lot of good detail on methodology and sample assessment instruments. Unfortunately their funding was cut and they were not able to actually carry out the project.
Seifer, S. D., & Connors K., (Eds.) (2007). Community campus partnerships for health. Faculty toolkit for service-learning in higher education. Scotts Valley, CA: National Service-Learning Clearinghouse.
Service Learning Magazine produced by the Center for Ethics and Social Responsibility at the University of Alabama. This periodical has great examples of service learning in a variety of disciplines.
Stoeker, R., Tryon, E. A., & Hilgendorf, A. (2009). The unheard voices: Community organizations and service learning. Philadelphia: Temple University Press, 2009. Chapter 10 elaborates on the Community Standards for Service Learning.