If you have extensive background knowledge of finance and investing:<p>Corner of Berkshire and Fairfax forum
<a href="http://www.cornerofberkshireandfairfax.ca/forum/index.php" rel="nofollow">http://www.cornerofberkshireandfairfax.ca/forum/index.php</a><p>Security Analysis subreddit
<a href="https://www.reddit.com/r/SecurityAnalysis/" rel="nofollow">https://www.reddit.com/r/SecurityAnalysis/</a>
Not really a similar dynamic to HN, but I highly recommend <a href="http://bogleheads.org/" rel="nofollow">http://bogleheads.org/</a> - especially recommend their wiki.
In some sense similar to HN, but built on Lobste.rs: <a href="https://bitmia.com/" rel="nofollow">https://bitmia.com/</a>