Here are links to the websites of professional associations likely to be of interest to you -- but don't forget that there are others! The membership applications are usually easy to find and download. In most cases, you can link to local chapters from the national association's site.
American Society for Information Science and Technology
New Jersey Library Association
New Jersey Association of School Librarians
The Society of American Archivists
American Association of Law Libraries
Art Libraries Society of North America
Association of Computing Machinery
Society of Competitive Intelligence Professionals
Association of Independent Information Professionals
North American Serials Interest Group
NJLA has a list of associations specific to New Jersey at: http://www.njla.org/resources/organizations.htmll