As the others have said, these are some of the ones I belong to (click on the names to go to their sites):
Romance Writers of America (any romance writer can join--no requirement to be published)
Science Fiction & Fantasy Writers of America (must be published by print, advance paying publisher in SF/Fantasy genre to join as a full member.)
Horror Writers of America (must be published by print, advance paying Horror publisher to join as a full member)
I'm also a member of the
RWAOnline chapter of RWA--this is an "all-internet" chapter with over 200 members from nine countries! It's got mega-published authors such as Sherrilyn Kenyon, Diana Gabraldon, JoAnn Ross, Claire Delacroix, among many others, as well as plenty of newbies, just getting started. Members hail from Canada, U.S., Australia, Germany, France, Japan, Barbados, England, and Sri Lanka (there might be one or two others, too. Can't remember for sure.)
Once you're multi-published, there's also
Novelists, Inc., which started out to be the stomping grounds of some RWA members, but has grown to include multiple genres.
Now, the "non-paying" groups--meaning they're just forums like this one to hang out and have all sorts of different authors in various fields:
Romance Divas
Writers BBS
Writers.net
All in all, there's LOTS of places to get your "joining" feet wet, so plunge right in and have fun!
