Ghostbusters West Coast is the official site of the fan fic franchise I belong to. Character profiles, art, and of course all of the GBWC fan fictions are available there!
The Ghostbusters Omnibus Fan Fiction Page is a joint venture between Brian Reilly, Ben King, and myself--the creation of an entire fan fic universe based on the Omnibus Timeline.
Ghostbusters.nuts is a collection of hilarious comic spoofing the Ghostbusters...and Ghostbuster fandom. It's run by Ben King, from an idea he co-created with Chad Paulson.
Ghostbusters.net is administered by Chad Paulson, and is another popular Ghostbuster message board on the web.
The Ghostbusters International Web Site. Administrated by Rich C. Roy (Spengs), it's the indispensible source of information about upcoming projects from GBWC and all of the GBI franchises!
Nightsquad.net is the official web site of the Ghostbusters: Nightsquad, the first and formost of the GBI fan fiction franchises. Just don't go on their message board if you offend easily 
.
The Nexus is the fan fiction and art site run by Nightsquad's Jen Spengler. In addition to Ghostbuster stories, it also features some imaginative song video scripts and and parodies, and concept art of the Ghostbusters as Pokemon.
Ghostbusters UK is a sister franchise to the GBWC, and my friends Ben King and Iain Bennett (also known as Kingpin and Sinister) are members, as well as really cool guys too!
Spook Central, created by Paul Rudoff, recently reopened for visitors (it's still archived, though). This is one of the best GB sites I've ever seen, with episode guides, the movie scripts, and loads of pictures.
Proton Charging is a great Ghostbusters news site run by Chris "castewar" Stewart.
The Real Ghostbusters Fan Page! Webmastered by Shiela Paulson, possibly the most prolific creator of Ghostbuster fan fiction. Many of the "facts" about the Ghostbusters families found in the Timelines and Fact Lists come from her fan fictions.
NYGB Tourguide is from ECTO-1, who lives in New York City, and is a great guide to all the sights of the movie filming
NYGB COMICGUIDE is also run by ECTO-1, and is a comprehensive guide to both the Now Comics of the 1980's and the current books by 88MPH. Even though he didn't mention my letters...(lol)
Ghostbusters Toy Archive is run by Like Venkman, and is a good source of information on all those wonderful toys, even the Filmation ones.
The Von Homborg Deutchendorf Family Web Page is a hilarious site devoted to Vigo the Carpathian's little-know family, including his twin, Lord Vego, and his cat, Snowball.
Labidolemur's Ghostbusters Fan Fiction Review features a wonderful Ghostbuster Canon List (slightly out of date, but it reminded me of things even I'd forgotten!) and some insightful insights into the characters, including some speculations about the Ghostbusters' religions and whether Egon has Marfan Syndrome. this list forms the basis of the Ghostbusters Fact List that Ben King created, and the Ectozone hosts
PKE Online is one of the oldest Ghostbusters sites on the web, and is run by Campi, a talented artist in her own right.