General Homicide Communities:
eromitlab is the the new community on the block. All things Homicide (from fic to icons to episode discussions) are welcome. Thus far eromitlab has been pretty darn successful. Even though I am a mod over there I think I'm still allowed to say that it is the best first place to go LJ for Homicide. (-: There are also several older general Homicide communities that are mostly dormant (hlots, homicide_lots, thewaterfront, dhappy).
Essays & Fic Recs:
Tim Bayliss essay at idol_reflection
Homicide introduction at crack_van
Homicide fanfic recs at crack_van
Luther Mahoney essay at eromitlab
Homicide Related Communities:
tommywestphall is the LJ community for the Tommy Westphall Multiverse which traces the web of TV crossovers created thanks to the crossover between Homicide and St. Elsewhere
Richard Belzer's character on Homicide (John Munch) moved over to Law & Order: SVU after Homicide. The character & the actor each have LJ communities, themunchies and belzonics respectively.
Other Related Communities:
police_drama - a catch all community for any police drama.
yellowtapeicons - accepts icons from any police drama.
l_and_o - not only is John Munch still on L&O:SVU but Homicide itself crossed over with L&O:Classic 3 times.
hbo_thewire - is the most active community for HBO's The Wire which was created by David Simon.
oz_interaction - Homicide producer Tom Fontana also created the HBO series Oz (ozslash &
oz_is_dead are the two other fairly active Oz communities).
Links on the Sites - The Link is a comprehensive collection of all news articles and sites about Homicide and various related shows. The only thing the site doesn't cover is the wide world of LJ.
The Board - on Homicide cases were listed on a white board (red for open, black for closed). This website has all the board data compiled.
The Glossary - a short entry on virtually every character, case, or detail that is important in canon, from Susan Aandahl to Emma Zoole.
11 Cents & Schism - Neither of these sites are accepting new stories but they are the two largest Homicide fanfic sites.
alt.tv.homicide at Google Groups - ath used to be the lifeblood of the Homicide fandom. It isn't really active anymore but the searchable archives at Google Groups are a treasure trove of information.
If you know of anything I've left out, please let me know.