I'd start a seed fund that specialized in startups driven by technical entrepreneurs and mentor them / provide them with connections to investors. HN would be the major channel for getting new startups to apply.
I'd change all amazon links to affiliate links (assuming they weren't affiliate links already, not that I've seen very many here). There are a boat load of posts devoted to books here, and lots of book recommendations going on outside those posts. The big book threads get linked to again and again.<p>The only other thing I can suggest that I think would appeal to the community would be to sell ads to ycombinator startups at ridiculously low rates. One to two ads per page, nothing obscene.
HN is already monetized. It's one of a couple effective vehicles for YC awareness. I have no doubt that many applicants first encounter YC via HN.<p>That's a radically different monetization model than you might be thinking of, but many other shorter term models would have a negative impact on the HN experience and the YC promotion effect.
Unless the ethos of the site were changed, you'd have to have any features limited to gold members limited because they're computationally expensive, and not just to encourage payment -- the way reddit lets gold members have different sort orders on eir profiles, or view more comments in one page. Arbitrarily picking (i.e. "you can't see dead comments unless you're gold") would make the site worse.
I would turn HN itself into a startup company. Have some dedicated people working on the problems of scaling, adding new frequently requested features, and community management. It could be monetized by a mix of relevant ads and paid premium accounts allowing access to additional aspects of the site.
Easy, charge for a monthly fee to access the site. Period. Sort of along the lines of Metafilter's one time fee, in order to keep the commentary and content both relevant and interesting you could raise the barrier to entry.
Primarily Google Ads (or equivalent).<p>If HN has reached some critical mass of readers I'd (in a craigslist-fashion) charge small fees for certain types of commercial posts (job postings, review my startup/webservice etc).
I know searching the site is something I want to do constantly. I would offer some sort of pay-for-search credits system or a membership $5-7 per month that simply lets me search.