There are many organizations all over internet which are useful to webmasters and other people on internet. This is a list of some of ones which I find useful.Americans For Computer Privacy - This is organization to take a look at if you are interested in privacy matters.
http://www.computerprivacy.org
Association of Computing Machinery (ACM) - One of oldest organization of all. This group is huge and has so many benefits that it's impossible to list them here. It can be highly technical, and tends towards theory and practice of computing. They have dozens of publications and for about a hundred bucks you get access to a huge online library of white papers and technical works.
http://www.acm.org
Better Ethics Online (BEO) - A great group all about ethics of online world. They have several lists of known spamming email addresses which can be used in filtering software.
http://actionsites.com/beo/index.html
Coalition Against Unsolicited Commercial Email - Want to learn about spam and how to prevent it? This is a great organization to join and join fight.
http://www.cauce.org
Cyber Crew - A group of volunteers which covers just about everything on internet. More of a users group than anything else.
http://www.cyber-crew.com
HTML Writer's Guide - This organization has lots of good web-based courses and a certification program (Certified Web Professional). This group (which has merged with International Webmasters association) has many other great features. Yearly members is about fifty bucks, and this gets you courses at half price.
http://www.iwanet.org
IEEE - One of very largest and oldest computer societies. In fact, computers are only a portion of what this organization offers. Thousands of papers are available online to members, and dozens of publications are published. This group tends to be highly technical and very in-depth.
http://www.ieee.org/portal/index.jsp