Founded in 1941 by Damon Knight (who is also responsible for founding the Science Fiction and Fantasy Writers of America, a/k/a SFWA), the National Fantasy Fan Federation (or more commonly, N3F) was originally conceived as a national organization for fans of fantasy & science fiction, which it still is, but it was never as popular as local SF clubs, and like many fannish organizations, took a serious hit to its membership once the Internet opened to the public and made it possible for fans to meet online instead of at conventions or through the mail.
Still, the N3F plugs on. Currently, the three hundred or so members publish a monthly newsletter, an APA that collates every two to three months, and eight ezines with varying publishing schedules and varying topics, ranging from reviews of books, games, movies, anime & manga, and TV shows to philosophizing about fandom and the interactions between fans and professionals. The focus is still mostly on science fiction and fantasy, but it has also expanded to include horror, anime, manga, and other media.
For more information, check out the N3F's website.