Reddit.com/r/haskell is the best subreddit. Pretty much any thread with more than 5 messages is worth reading carefully. Pinboard has some great contributors for haskell / agda / Coq. Delicious has dwindling volume of new bookmarks. after multiple usability gaffes.
HaskellNews.org, kinda like alltop.com for haskell Planet.Haskell.org reprints complete text of several dozen RSS feeds and is dependent on the bloggers keeping technical content separately tagged or somehow segregated. So you'll see some sysadmin, data mining, lisp/scala content. Not strictly germane but not uninteresting.
Not speaking without double negations, not making it undifficult to pin me downHNsearch.com: worth looking at all haskell-related activity a couple times a week, decent volume of insightful posts. Google Plus is gaining traction, with first-rate haskellers to follow. A couple recently joined Facebook, let's see how haskell Walls evolve.
Mailing list: Haskell-Cafe. Open Google Groups and read any thread that has "M < messages < N" where M is 5 or 10, N is 20 (20+ is yak shaving domain). Google Groups also lets you read, say, all of Conor/Conal/Oleg/CC's posts. GHC commits: http://www.haskell.org/pipermail/cvs-libraries/ This is its own firehose, the Simons et al. are developing furiously. Shelarcy keeps close tabs on commit messages and GHC trac issue tracker, unfort'ly you need a native Japanese developer to deep comprehend. Prolific tweeter for Category Theory/algebra: José A. Alonso .
IRC freenode channel: You could spend the rest of your life here, you'd be an expert on haskell and parsing broken sentences/typo's. Transcripts Microsoft academic Search. Spend the rest of your life here, too.
Not mentioned:
• Stackoverflow/stackexchange,
• Beginners and other haskell.org lists,