An organization to add to yesterday's Mystery/Suspense/Thriller category (thanks to Alan Orloff) is International Thriller Writers. Members are able to add profiles, photos, website urls, and other information to The Big Thrill website. I'm not currently a member of ITW, but have been thinking about joining (especially since my current project is more thriller than mystery).
I also neglected to mention the many regional and local chapters of Mystery Writers of America and Sisters in Crime. Here, for instance, is Sisters in Crime Chicago. Although SinC does not sponsor blatant self-promotion on their websites, they do announce author news and appearances, and many post author bios for their members.
To hop away from the mystery world now, general writing organizations (not genre-specific) often provide multiple ways for an author to "get the word out." Northern Colorado Writers includes all genres of writers, as well as editors, publicists, journalists, etc. The NCW website displays a short bio, as well as an expanded member profile. This organization sponsors a writers' conference in the spring, which is where I gave my "Let's Write a Mystery" workshop.
Colorado has more. In the Denver area (but including members from all over Colorado and nearby states) Rocky Mountain Fiction Writers offers special programs, an excellent newsletter, and September's Colorado Gold conference and its associated writing contest. The Friday night book room event gives all attending authors a chance to chat about, sell, and sign their books. On the RMFW website, authors may add information to the Published Authors section and to the Member News page.
Pikes Peak Writers is centered in the Colorado Springs area. Although I'm not a member and can't speak to all of its advantages, it's another good example of an organization that sponsors a highly-recommended annual conference (and writing contest) and offers its members ways to promote their works.
There are writers' organizations of this type in most states (even others in Colorado I haven't mentioned). Why would you want join one of these groups? I think they're important for networking and making new friends; finding conferences, workshops, programs, and critique groups close to home; and enjoying the promotional options given members in newsletters and on websites.
Do you have an excellent writers' organization in your state that you'd care to recommend?