As the title says :) I think in asking this question I am excluding sites that are exclusively devoted to a particular character’s RP log. They can be RP-related of course but I am looking more at things that an uninvolved third party can find useful
The ones I am aware of are:
[li]http://echobazaar.wikidot.com/ (Starting to verge on slowly becoming inactive)[/li]
[li]Delicious Guide to Fallen London (Not precisely Active but remains useful in a static sense)[/li]
[li]http://deliciousfriends.tumblr.com/ (General RP reference)[/li][/ul]
And… that’s about it…
Lots of good tumblr have gone dormant :( http://scandal-and-indulgence.tumblr.com/ and http://fifthcitytea.tumblr.com/ hardly ever update anymore and http://plaiddragon.tumblr.com/ has disappeared entirely :((
There are a number of useful Twitter feeds, especially since the Failbetter staff tweet regularly (and sometimes post content / links to articles there that don’t get mentioned elsewhere).
…each FB staff member probably has their own Twitter, too. Some of the FL characters have Twitters, though I think those were mostly for one-off live RP events.
There’s also a couple of Reddit pages, I think?
TV Tropes also has pages for Fallen London and Sunless Sea.
Personally, I also find the discussions of FL and Sunless Sea stuff on Emily Short’s blog to be quite interesting (she’s one of the guest writers):
Sorry, I’m in a rush right now, but I think the other guest writers have also written about their parts & experiences.
Notable and not yet mentioned:
You’re forgetting the IRC!
edited by Cecil on 9/16/2015
This one: http://echobazaar.wikidot.com/ has actually been inactive a while, or close enough to count. it’s not reliable enough to use, so save some time and use the other one.