The SFWA created the Nebula Award; its work has benefited writers; and its website is a mine of information on speculative-fiction for fans, with scores of reading lists
Founded in 1965 by Damon Knight, Lloyd Biggle jnr, and other science-fiction writers, the SFWA now has over 1200 members. But it's influence is felt right across the SF field, and is not solely limited to its immediate membership.
The most visible and perhaps far-reaching manifestation of the SFWA is the annual Nebula Awards anthology. Each year the membership of professional writers and editors award is given to the best novel and short fiction published in the USA the previous year. the winning short-fiction and selected runners-up are collected into an anthology. This unique 'Best of the Year' differs from the regular collections in being determined by over 1000 people, and for many people, including the writer of this article, is their first glimpse into the world of speculative-fiction, encompassing, science-fiction, fantasy, horror and slipstream.
While relatively inferior stories have sometimes won the Nebula, and good stories have missed out, the roll-call of Nebula winners is an outstanding one; Frank Herbert's Dune, Larry Niven's Ringworld, William Gibson's Neuromancer to Neil Gaiman's American Gods are just a few of the classic winners.
From 1965 to 1968, only science fiction stories were eligiable for the Nebula award, but from 1969 fantasy stories began appearing on the ballot (the first winner was as early as 1970 -- Fritz Leiber's 'Ill Met in Lankhmar') and the demographic of the SFWA gradually changed, until in 1992 it was re-named The Science Fiction and Fantasy Writers of America.
This has not only reflected the changes within spec-fic, as fantasy has outstripped SF in popularity, but may also have influenced the field as a whole as writers like Kelly Link who work primarily in short fiction --rather than the stereotypical trilogy of fantasy-- have been drawn to the field in ways they might not have, had the SFWA and other influential bodies such as the Clarion Workshop restricted themselves rigorously to sci-fi.
Four times a year the SFWA publish the Bulletin, a journal featuring columns, articles on SF, and market reports. It's an invaluable guide to those wishing to understand the field as it is. Details of how to suscribe can be found on the SFWA website.
In addition, there are links to publications such as the latest Nebula awards anthology, and the SFWA European Hall of Fame
One of the finest features of the SFWA website, itself an invaluable treasure trove for those wishing to understand sci-fi and fantasy, is the list of links, and particularly of suggested works for those wishing to read further. While many of the works of more established writers name-checked do link to on-line purchasing, the reader wishing to economize can get an idea of names and titles and make a note for their next library visit. There are also an increasing number of links to works available for free, under creative commons licences.