By conducting a search for internships in say, Massachusetts the site gives you all of the relevant search sites with internships listed particularly for Massachusetts. A searchable database allows you to search hundreds of internship opportunities. The site has recently been updated so look for more opportunities here in the future. Another general listings site. They feature internships in health, education, nonprofits and social services.
Applications are due in spring.
See site for further details. This is the Department of State's internship index. Some are domestic, others abroad, but most are unpaid. Choose from a broad spectrum of categories such as environmental affairs, human services, international affairs, and public interest and citizen affairs. GreenForNewEngland.org Environmental Federation of New England hosts this site.