12days_of_clois : Challenge Community centered around the Clark/Lois pairing
agoodsoldier : Anything about Jason Todd
all_dc_related : Anything DC
allaboutclark : Anything about Clark Kent
batcat_fic : Bruce Wayne/Selina Kyle, Bruce Wayne & Selina Kyle
batfic : For fic featuring any Batman character prominently.
batfic_contest : Challenge Community centered around the Batclan
bertinelli : Anything involving Helena Bertinelli (Huntress)
bigfreelove : Big Barda/Scott Free
batknights : Dick Grayson/Bruce Wayne, Dick Grayson & Bruce Wayne
bats_femslash : Femslash about the female members of the Batclan
chlark_crazed : Smalleville Chloe/Clark stories.
chlollie : Anything related to Chloe/Ollie on Smallville
dc_central : For all fics DC-related, any rating or pairing.
dccbatflash : Batman/Flash stories.
birdsofprey_fic : Anything Birds Of Prey
boostle : Ted Kord/Michael Jon Carter, Ted Kord & Michael John Carter
brexfic : Lex Luthor/Bruce Wayne, Lex Luthor & Bruce Wayne
cap_ironman : For anything related to Captain America (Steve Rogers) and Iron Man (Tony Stark) (not DC but an awesome pairing)
cloisfic : Clark Kent/Lois Lane stories.
comics_genfic : The comm is for any story that isn't focused primarily on the sex. It can have sex of any variety in it, it just shouldn't be the focus of the story.
comicslash : Slash with comic book characters
darkknightfic : Anything connected with the Nolan movies.
dcu_freeforall : Challenge community covering the entirety of the DCUdead_robin : Anything about Jason Todd
deathstrokes : Anything about Slade Wilson
escarabajo_azul : Anything related to Jaime Reyes a.k.a. Blue Beetle III
flash_rogues : For anything relating to the Flash Rogues' Gallery
glcorps : Anything related to the Green Lantern Corps
gothamgirls : Anything related to the women of the Batclan, the Birds of Prey, and other heroines associated with Gotham
guy_kyle : Anything with Green Lanterns Guy Gardner and Kyle Rayner.
hal_kyle : Anything with Hal Jordan/Kyle Rayner (slash or friendship)
jl_fic : any fic in the DC Animated Universe
jla_fics : All fic with at least 1 member of any Justice League team, past or present
jla_united : Everything Justice League (and every other superhero team)
jlu_slash : Any slash fic, art, or graphics for Justice League Unlimited
jsa_allstars : Any fic involving the Justice Society of America, past or present.
knivesandlint : Related to movieverse Joker.
legion_fic : All fic for the Legion of Superheroes
legionnaires : Anything about the Legion of Superheroes
mrsarcastic_tim : Anything with Tim Drake.
nowweretwo : Movieverse Jim Gordon/Bruce Wayne.
nwo_now : For anything fitting into the comm creators' "New World Order" - Essentially, the entire JLI living on a quiet suburban cul-de-sac.
old_school_clex : Slash comm which concentrates Clark Kent/Lex Luthor in the first three seasons of Smallville
oliverxthea : All fic about Oliver/Thea from Arrow.
ollieville : Anything with Smallville Oliver Queen (Green Arrow)
persist_heroes : Tim, Cassie, Kon and Bart- the four Young Justice members that became Titans. Het and gen only.
piper_trickster : Pied Piper/Trickster, Pied Piper & Trickster
quiddler_fic : Anything related to Harley Quinn/Riddler.
reeveverse : For any fic involving the Superman movies with Christopher Reeve.
robincest : Stories pairing any of the Robins (Dick Grayson, Jason Todd, Tim Drake, Stephanie Brown, Carrie Kelley) together.
routhslash : For slash featuring Brandon Routh (Superman in Superman Returns) or his characters.
roydick_slash : Roy Harper/Dick Grayson, toon or comics
royxtim : Roy Harper/Tim Drake, Roy Harper & Tim Drake
secondbananas : For fic featuring obscure DC characters. The perfect place for that Etta Candy/G'nort you feel compelled to write! (I love this comm)
so_very_super : Superman fics of all sorts.
superman_fics : Anything about Clark Kent.
superman_return : Anything based on the movie Superman Returns.
supersfic : Anything related to anyone in the Superman family of characters.
sr_slash : Clark Kent/Richard White, Clark Kent & Richard White from Superman Returns
sv_fanfic : Comm for Smallville fanfic, vids, and art. Not just Clex, but a lot of different SV pairings.
sv_slash : Another Smallville slash comm. Any SV slash pairing is acceptable.
teentitan_slash : Toon Titans only...no comics
thegreenarrow : All Arrow Clan related ficc
tim_cissie : Tim Drake/Cissie King-Jones (Arrowette)
timkon : Tim Drake/Kon-El
titans_together : Any incarnation of the Teen Titans, including the cartoon.
unforeseen_love : Smallville Oliver Queen/Clark Kent, Oliver Queen and Clark Kent
wfslash : All fic for the Superman/Batman pairing
we_love_dick : Anything about Dick Grayson
wonderwomanlove : Anything about Wonder Woman
worlds_finest : Clark Kent/Bruce Wayne, Clark Kent & Bruce Wayne
If you know of any I'm missing, please let me know in comments and I'll hasten to add them!