Astrum Society - A forum-based society that has different class hierarchy levels; you can join classes and fora at or below your level within this hierarchy. There is also an All Class Forum that members of all classes can additionally use to communicate. Accepts supervised tests for purposes of admission, but also "rigid" unsupervised tests, such as the Mega and Titan tests. Membership is currently 100% free.
International Lewis M. Terman High-IQ Society - The International Lewis M. Terman High-IQ Society encompasses four high IQ Societies founded by Ronald K. Hoeflin, Ph.D.: Top One Percent Society (99%ile), One-in-a-Thousand Society (99.9%ile), Epimetheus Society (99.997%ile) and Omega Society (99.9999%ile). See elsewhere on this site for listings for each of these groups. While each group has its own e-mail discussion list, ILMTHIS has a separate list that is open to any member of these four high IQ societies. NOTE: You cannot join the International Lewis M. Terman High-IQ Society without joining one or more of these other 4 societies, and if you join one or more of the 4 societies, you are automatically a member of ILMTHIS. All 4 of the above societes are now 100% online and 100% free to join. There are no fees of any kind. I highly recommend them all; they are very civil, and I have made a number of real friends through them.
The Smart Life - A social networking membership site created by a Mensan. "The world needs a place for us smarties to get to know each other, and to share our smart lore; the best websites, books, music, movies, TV, games, places, food & drink. For members of Mensa and invited friends only, 18+ years old. Please join us!"
Ancient Cryptography Group - This is a Mensa SIG (Special Interest Group) that is totally free and of course 100% online. You do not have to be a member of Mensa to join. However, at the request of the group's administrator, I provide a brain teaser that you need to answer in order to find the actual link for the group.
VINCI - "VINCI is a fun and friendly online group for anyone with an interest in creating and solving novel and unusual puzzles as well as a passion for creativity in general. Founded in the spring of 2003 it has blossomed into a community of over 200 members from all over the globe." Please note that Vinci is NOT a high IQ society.
National Puzzlers' League - Recommended for SERIOUS word puzzle enthusiasts. Not an IQ society, but most if not all League members surely would qualify as "high IQ". This is an inexpensive and excellent group for word puzzle fans (cryptic crosswords, cryptograms, anagrams and much more). The NPL has excellent online features, including puzzle solving tools, a print newsletter (The Enigma) with puzzles and answers, and regular gatherings. "The NPL was founded in 1883, and is the oldest surviving organization of puzzle enthusiasts in the world."
Science Fiction and Fantasy SIG - The Science Fiction and Fantasy SIG (Special Interest Group) of American Mensa has been in existence since 1976. The group's publication is the InterdiMensional Journal, which costs $10.00 for 8 issues ($16.00 in US funds if you are outside of the USA). Mensa membership is not required to subscribe to the Journal or participate in the SIG.
The InterdiMensional Journal is loaded with book, movie, and television reviews, artwork, poems, and short stories. It's just a lot of fun, and you really can't beat the price.
Acephalic Swine & Stupid Parrots - Satire/parody-oriented free e-mail discussion list maintained by Richard May, who is an active member of the Mega Society and other groups. You must be age 21 or over to join this group. As with the Ancient Cryptography Group, I have created a brain teaser that you must solve in order to get to the group's main page. The list is extremely active, with 5469 messages in 1/08 as an example. I am told that somewhat anti-semitic remarks are occasionally made in this forum, unfortunately.