Detention Watch Network 
http://www.detentionwatchnetwork.org/
The only national coalition in the U.S. that addresses the immigration crisis head-on and helps detainees and their loved ones make their voices heard. Formed in 1997 in response to the rapid growth of the immigration detention system in the United States, DWN is a network of individuals and organizations working in support of, and in service to, immigrants in detention.

No More Prisons 
http://www.nomoreprisons.org
The mission of the Prison Moratorium Project (PMP) is to explore and implement strategies that will bring about a society less dependent on prisons and incarceration.  They work locally and nationally to stop prison expansion and mass incarceration, and re-invest resources into communities most impacted by criminal justice policies through educational programs, alternatives-to-incarceration initiatives, housing and sustainable economic development.

Prison Activist 
http://www.prisonactivist.org
Committed to exposing and challenging the institutionalized racism of the criminal injustice system. They provide support for educators, activists, prisoners, and prisoners' families. This work includes building networks for action and producing materials that expose human rights violations while fundamentally challenging the rapid expansion of the prison industrial complex.