Stargate information, reference, and multimedia sites.

Stargate Information Sites
MGM: Stargate SG-1 - The official MGM site.
Stargate Command - Join the SGC at the official Showtime site.
RDAnderson - Richard Dean Anderson's resource-filled Stargate site.
Starguide - Excellent episode guide and news source.
Stargate Nebula - Comprehensive quote collection.
Sphinx Stargate - UK-based resource.
The Fifth Race - Burgeoning information and multimedia site.
The Serpent's Lair - Reviews of all episodes.
Netpicker's Netguide - Dissecting the details of Stargate.

Stargate Reference/Research Sites
Stargate SG-1 Research/Reference - Detailed log of all canon information.
Stargate Dictionary - Very comprehensive.
Goa'uld Dictionary - Speak the language of the gods.
The Goa'uld Homeworld - Meet the system lords.
Digging Up The Stargate - Egyptology and Stargate.
The Truth Behind Stargate SG-1 - Glossary of people and terms, real and canon.
Encyclopedia Mythica - The mythology behind the mythology.
Chevron 26 - Lots of information.
Sublevel 28 - Breaks down information by SGC locations.
Stargate Central - Good reference site.
The SGC - Stargate research and reference site.

Stargate Transcript Sites
SG-1 Fans Transcripts - Transcripts for the majority of episodes.
StargateFan Transcripts - Smaller collection, mainly from seasons 3 and 4.

Stargate Multimedia Sites
P3x-595 - Huge episode image and sound capture archive.
Stargate Episode Archive - Downloadable versions of every episode.
The SG-1 Files - Downloadable episodes and videos.
Bri's Wallpapers - Large collection of themed wallpapers.
Daniel In The Lion Pit and Good Morning, Campers - Hilarious photo manipulations featuring Daniel and Jack.
Snuffles Gate Command - Cute bear-based photo manipulations.

Stargate Fanvids
Whatever Dials Your Gate - A large collection of Stargate music videos.
D2 and HM's Music Vids - Home to the first Stargate fanvids.
Jolinar's Music Videos - More SG-based music videos.
Rhian's Collection - Many more SG-1 fanvids.
Whimsy's SGVids - Several fanvids, including the Dancing Spacemonkey.
Suz's Vids - Shipper, team, and character fanvids.

Know of a site that should be listed here? Tell me.

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Stargate SG-1 and related characters are © Showtime/Viacom,
MGM/UA, Double Secret Productions, and Gekko Film Corp.