Non governmental organizations in the US
American Immigration Lawyers: AILA is a non-profit Organization affiliated with the American Bar Association. The page provides information on U.S. Immigration issues from a legal perspective.
Interaction: Interaction is a group of non-profit organizations dedicated to issues affecting the poorest populations in the world. They have a Committee on Migration and Refugee Affairs and so does their page provide access to information on the subject.
The Federation for American Immigration Reform (FAIR): FAIR is a national, nonprofit, public- interest organization of concerned citizens who share a common belief that US immigration policies must be reformed to serve the national interest. FAIR's belief is that the United States is receiving more immigrants today than at any time in its history, affecting every aspect of national life. FAIR considers that large-scale immigration is not serving the needs and interests of the country.
U.S. Immigration by Nerd World Media: Gateway to U.S. Immigration resources, law firms, do-it-yourself immigration services.
American Truths: Organization concerned with indigenous and migrant communities. It looks to understanding their history based on such sources as oral traditions.
California Rural Legal Aid. Non-governmental organization benefitting agricultural workers in California. the website contains legal inforametion, recent news and a section regarding guest worker programs.
The Center for Immigration Studies is a non-partisan, non-profit organization founded in 1985. It claims to be the nation's only think tank devoted exclusively to research and policy analysis of the economic, social, demographic, fiscal, and other impacts of immigration on the United States. It hosts an ample website with sections on history, illegal immigrtion, population environment, refugees, trade, guest workers, etc., with articles that promote the view that there is too much immigration into the United States.
Center for Gender and Refugee Studies University of California, Hastings College of the Law Website dealing with asylum and refugee issues from a gender perspective.
National Coalition for Dignity and Amnesty of Undocumented Immigrants. Organization that promotes a General Amnesty for a large group of undocumented migrants in the Unites States.
Houston Catholic Worker. Casa Juan Diego's publication. Catholic organization for migrants. This website contains directories and other useful information as well as religious messages for migrants.
National Immigration Law Center. A national support center whose mission is to protect and promote the rights of low income immigrants and their family members.   NILC staff specialize in immigration law, and the employment and public benefits rights of immigrants.  The Center conducts policy analysis and impact litigation and provides publications, technical advice, and trainings to a broad constituency of legal aid agencies, community groups, and pro bono attorneys.  NILC maintains offices in Los Angeles, Oakland, and Washington, D.C. and operates the Sacramento policy office for the California Immigrant Welfare Collaborative.
Center for Migration Studies. The Center for Migration Studies of New York (CMS), founded in New York in 1964, is one of the premier institutes for migration studies in the United States. It is committed to facilitating the study of sociodemographic, historical, economic, political, legislative and pastoral aspects of human migration and refugee movements. At this website viewrs may purchase publications and find links to similar research organizations.
Farmworker Justice Fund, Inc.       For twenty-two years, the Farmworker Justice Fund, Inc. ("FJF") has been helping empower migrant and seasonal farmworkers to improve their wages and working conditions, labor and immigration policy, health and safety, and access to justice.  Website includes legislative news, safety and health information, H2 program and labor law information.. 
The American Immigration Law Foundation (AILF) was established in 1987 as a tax-exempt, not-for-profit educational, charitable organization. The Foundation is dedicated to increasing public understanding of immigration law and policy and the value of immigration to American society; to promoting public service and excellence in the practice of immigration law; and to advancing fundamental fairness and due process under the law for immigrants. A good legal source on the issue, also offers diverse opinions articles on the issue.
The International Relations Center is working to make the U.S. a more responsible member of the global community by promoting progressive strategic dialogues that lead to new citizen-based agendas. Very ample web site with ample information and opinion pieces on a large array of issues of US Foreign Policy, including immigration. I suggest you use the search capability of the site to locate these text on immigration.