X-Men: Links
Edited to add on April 13, 2015: I have not tested every link, but I am sadly sure many are dead. I'll leave this here for historical purposes if nothing else.
Itty Bitty Archives
http://www.comicfic.net/
http://www.comicfic.net/fic/dex/zero01.htm
Comic Book Fan Fiction Awards CFAN
http://www.subreality.com/cfan/cbffa.htm
Subreality Central Archives and Links
http://www.subreality.com/sc.htm
Marvel Fanfiction Archive
http://www.marvelfanfiction.com/
Outside the Lines
http://lists.topica.com/lists/outsidethelines/?cid=13096
A mailing list for comics based fan fiction
The Wolverine and Rogue Archive
http://www.wolverineandrogue.com/fic/
X-Men Hero Cyclops Fiction Archive
http://www.dreamwater.org/scottsummers/fanfiction.html
Wolverine and Jubilee
http://www.wolverineandjubilee.com/Archive.html
The Fonts of Wisdom
http://home.att.net/~lubakmetyk/index.htm
X-Men The Movieverse Fan Fiction
http://www.xmmff.com/
http://community.livejournal.com/xmmff/
(Originally and still a Yahoo mailing group)
X-Fiction
(doesn't seem to have an archive)
(Originally and still a Yahoo mailing group)
http://community.livejournal.com/xfiction/
X-Men The Movie Fiction
http://www.ktnb.net/xmovieslash/
Adamantium Awards
http://home.earthlink.net/~adamantium_awards/
X-Day Contest Fic
http://www.xday.info/
X-Men: X-rated fic; splash page typically carries an X-rated piece of art.
http://www.merchi.org/dxea/
Moving Pictures
http://www.users.bigpond.com/storysmith/movingpictures/
Brenda Antrim’s Fiction, now Castle's Keep
moved from http://www.bantrim.net/ to http://www.castleskeep.net/
Her X-men story links on castleskeep don't work anymore, but can be found on Archive of Our Own, where she posts under the pseud Glacis
http://archiveofourown.org/users/glacis/pseuds/glacis/works?fandom_id=839
The DMZ
http://www.offpanel.net/dmz/
Creed Cascade’s and TJ’s fiction
http://www.insaneasylum.slashfanfiction.com/fiction.htm
Khaki’s Med Lab
http://khakigrrl.fandomnation.com/
Mo’s Fic
http://www.angelfire.com/comics/mo/
Ridesandruns' Fic
http://www.fanfiction.net/u/485506/
The Medicine Wheel
http://www.themedicinewheel.net/
The Medicine Wheel is now permanently offline and Min has retired from active participation in fanfiction. You can still find her fanfic at https://www.fanfiction.net/u/106720/Minisinoo
The Medicine Wheel Favorites Page
http://www.themedicinewheel.net/recs.html
a shame this link is dead, it was a great resource
Uncanny X-Men -- summaries of every X-verse comic book issue
http://www.uncannyxmen.net/
DRG4’s X-Men: The Animated Series information
http://hometown.aol.com/drg4/x.html?f=fs
X-Men Evolution Series information
http://www.tvtome.com/tvtome/servlet/ShowMainServlet/showid-1251/
Kataclysm's X-Men: Evolution Page
http://evolution.eracerx.com/
TV.com's X-Men Evolution Page
http://www.tv.com/x-men-evolution/show/1251/summary.html
The Marvel Directory
http://www.marveldirectory.com
http://www.marveldirectory.com/individuals/c/cyclops.htm
Superhero Hype
http://www.superherohype.com/
Glass Onion Fic Archive
http://glassonion.populli.org/
Left Turn at Westchester RPG (now defunct, but the fic's still up)
http://leftturnatwestchester.yuku.com/ or
http://p087.ezboard.com/bleftturnatwestchester
http://community.livejournal.com/ltaw/
Comixfan
http://www.x-mencomics.com/xfan/
The X-Axis
http://www.thexaxis.com/
Marguerite's Fic
http://4dw.net/marguerite/chaostheory.html
The Fannish Butterfly -- interesting essays
http://www.trickster.org/fannishbutterfly/index.html
Fanfic Symposium -- interesting essays
http://www.trickster.org/symposium/
Danger Room Fic
http://www.danger-room.net/
Katt's Fic
http://www.madweasel.com/kattsaerie/index.htm
Mara's Fic
http://mara.ink-and-quill.com/viewstory.php?sid=214&i=1
Tin Hut Lady's fic:
http://library.thetinhut.com/
Fringe Element -- interesting essays and reviews
http://ljconstantine.com/column9.htm
Now-dead XM links:
http://www.fanficweb.net/directory/index.html
http://dolphinhaven.50megs.com/index.html W&R fic
http://www.blufiction.org/ Blu's fic
http://www.thesandbox.org/sandboxstorypage.htm Heather’s fic
http://alykat.hispeed.com/rogue/index.shtml Down Home Charm Rogue Archive
http://www.ficorama.net/otherfic.htm Elizabeth’s fic
http://www.wxfonline.com/frames3.html Wolverine X-Fiction