HN who wants to be hired/is hiring threads have so far the best ROI I've found.
(Just kidding)
But, worth pointing out: A job board is only good when it's low-spam; and that does require some moderation. If we start getting lots of spammy / uninteresting jobs; or job posts get lots of spammy applications; the usefulness of these threads will errode.
A few hours after I posted my first comment on the ‘who wants to be hired’ post I got ‘referred’ by another person (whom I don’t know) to a jobs site.