The two I visit most (after http://browncoats.serenitymovie.com) are http://www.fireflywiki.org/ and http://still-flying.net/

Others to include would be:
http://fireflychinese.home.att.net/
http://signal.serenityfirefly.com/signal.php
http://www.fireflyfans.net/

And the country specific
http://www.serenitymovie.com.au
http://www.cantstopthesignal.co.uk/


(Maybe http://whedon.info and http://whedonesque.com as extras?)

Hmm, yes. I think that would be it.