Ask HN: How can a boot-strapped startup market without spending money?

I launched a small startup a few months ago called Talentopoly.com. I spent a few hundred dollars on advertising in the first few months and it seemed to help bring people to the site. Without a source of revenue though a long-term marketing budget is not sustainable. I use Twitter, my blogs, guest posts, etc. to draw attention to the site and get the word out.

I'm interested to hear from the HN crowd other ways to market a boot-strapped startup like mine without spending money every month on advertising. What are some other ways to market a startup? Thanks in advance.