Most of the stuff I read is actually economic, not necessarily financial. For that: http://economistsview.typepad.com/ is about as good as it gets. Although I would recommend ignoring the frequent Krugman reposts. The comments are also usually dominated by 3 or 4 very opinionated posters. Also http://www.nakedcapitalism.com/ for general news/interesting headlines. https://www.statnews.com/ is great for healthcare.

One thing I see every once in a while on HN is people with the belief that they can spend a week or two knocking out an algorithmic trader and start raking it in. In order to break this illusion I would recommend: http://financial-math.org/ http://www.quantresearch.info/

And in terms of investing, Bogleheads is of course incredibly popular but still the best way to get investing safely and quickly.

EDIT: I'd also like to say that the Wall Street Journal is pretty invaluable but I have a subscription. The google loophole closing may make that a more difficult source for the layman.

There are various finance blogs, but discussion sites tend to be a disaster - actual information is worth money and not given away for free, so most people are just "talking their book".

A very niche community though. Most prefer sticking to Bloomberg.