WebZines
Analog SF Magazine Home page of long-lasting sci-fi magazine
Asimov's Home page of the magazine named for the great master himself
Dragon Page Unique SF/Fantasy radio talk show with an online feed
Hologram Tales Good sci-fi webzine hosted by SF Crowsnest
Science Fiction & Fantasy World One of the best on-line zines
Science Fiction Studies Zine with academic resources from DePauw University
Science Fiction Weekly SciFi.com's highly-regarded webzine
SciFi Dimensions Sci-fi site with a little bit of everything
Scifind UK speculative fiction site with DVD news and reviews
ScifiSlacker Speculative fiction news and reviews site
SciFiSpace Speculative fiction site with news, info, chat room, etc.
SF Site Comprehensive, informative and well-written webzine
365 tomorrows Collaborative site publishing a new piece of short speculative fiction each day

General Reference
AudioBooksForFree Free sci-fi audiobooks including a handful of classics
Definitions of Science Fiction More than fifty definitions of sci-fi from authors
epguides.com An index to episode guides for sci-fi/fantasy TV shows
Feminist Sci-Fi Linked bibliography of feminist sci-fi, fantasy and utopia resources
GEOS (SF Television) Comprehensive opinion survey of current shows
Internet Movie Database Lots of info about films of all kind, including sci-fi
Internet Speculative Fiction DataBase Massive database of genre literature
Locus online Extensive database, news, reviews, award info & links
Quiet Earth Dedicated to genre film and all things post apocalyptic
Saturn Awards Sci-fi awards organisation focussing on film and television
Sci-Fi Movie Page Movie & DVD Reviews, trailers & clips,  and news on upcoming movies
Science Fiction & Fantasy Writers of America Pure sci-fi class with no dross
Science Fiction Awards Watch Monitors and discusses sci-fi awards
SF Booklist A good user-friendly sci-fi/fantasy bibliography
SciFan Books & Links Terrific resource for fans of sci-fi literature
SciFi 2000 Off-beat sci-fi stuff like video covers and fonts
Taormina's Sci-Fi Guide Nifty guide at the Northern Virginia Community College
Technovelgy.com Where science meets fiction in classic SF literature
Ultimate SF Web Guide A vast collection of sci-fi resources
Variety SF A blogspot specialising in sci-fi literature, with plenty of short fiction
Wikipedia SF Television On-line encyclopedia with lots of info on sci-fi TV
(See also Wikipedia SF Films and Wikipedia SF Novels)

Search Engines/Directories
DirectoryScifi Well organised online science fiction directory.
Google SFF Most comprehensive and up-to-date directories on the net
SciFi Source Comprehensive directory of sci-fi sites
SF Crowsnest Europe's premier SFF website has a searchable directory
Speculative Vision Good directory covering all speculative fiction genres

Other Lists
ArtsForge Sci-Fi 100s Artistic community site with sci-fi books and films lists
Boston Globe TV 50 A one-at-a-time SFTV top 50, starting at the end
Carver Recommended Author Jeffrey A Carver lists his SFF recommendations
Cinescape Top 100 Greatest sci-fi, fantasy and horror films of all time
Classics of Sci-Fi Survey of classic sci-fi books by James Wallace Harris
Cult TV Top 100 Fabulous 'cult-TV' list based on poll of festival delegates
Darkweb Online An interesting list of the Top 100 Sci-Fi Films
Dozois Recommended Leading sci-fi editor Gardner Dozois' recommendations
Gamma Zone 100 A personal Top 100 SF novels list with too many pop-ups
Gunn's Basic Library James Gunn helped bring academic credibility to sci-fi
IMDb Sci-Fi Top 50 Top 50 and Bottom 10 SF movies with links to the database
Internet Book List A clever online database where visitors can rate titles by genre
Internet Top 100 SF/F The net's top SFF poll compiled by Tristrom Cooke
ISFDB Top 100s Book lists based on speculative fiction awards/nominations
Locus Best Novels Respected readers poll of best pre-1990 SF novels
OFCS Top 100 Films A good list from an online critics group, but not much else
Pringle's Top 100 Somewhat dated list of David Pringle's Top 100 SF books
Rate-it-All Films Allows visitors the chance to vote on their favourite genre films
Raven's Top 100 Poll Pop-up riddled list of mainly fantasy books
Renegade 100 SciFi List of top 113 sci-fi "thingies" from the Renegade club
TV.com List of the Top 100 sci-fi TV shows as voted by TV.com visitors
Wanderlist Favorites List of 70 sci-fi movies with online voting facility

The 1950s
Comic Kingdom Joe Sarno's 'Science Fiction on Television in the 1950s
Public Domain Torrents Download cheesy public domain sci-fi movies and serials for free
Roaring Rockets Site focusing on Captain Video, Tom Corbett & Space Patrol
SciFiFree.TV Free online video stream showing mostly older public domain sci-fi
Solar Guard Comprehensive 1950s sci-fi TV site and discussion page

Clubs & Other Stuff
Denver SFF Book Club Informative site run by prolific readers
Galaxiki Incomparable interactive site where visitors can help create a fictional online galaxy
New England SF Association Another book club with a good core reading list
Science Fiction Book Club Top 50 SFF list from online book club