The library/information profession is richly endowed with organizations devoted to advancing the improvement of library and information services. Membership information/applications for some are given in the pages that follow; for others, URLs and/or phone numbers are provided so that you can download or request forms. The ALA form that you should use can be found on the New Jersey Library Association Web site, and actually gives you a dual membership in both for a great bargain price ( http://njla.org/joinnjla/joint_app.pdf). There are more associations than we can introduce you to here, but you should be able to locate one that fits your area of interest, no matter how specialized (see the Bowker Annual for a list). Just to give you an idea of some that are omitted from this compilation: American Film and Video Association, American Theological Library Association, Association for Educational Communications and Technology, Catholic Library Association -- and on it goes!
There are also a number of associations in closely related areas, e.g., ARMA for records managers, ACM for computing, the Information Industry Association, the Association for Competitive Intelligence, to name a few.