"Reference worthy content" is a phrase you'll hear a lot in the SEO realm. The intent behind the statement is simple - build content that people will be likely to cite when they create works on the web. Parsing the motivations that inspire those citations, however, is anything but obvious. Tonight, I thought I'd try to list features that make content "reference worthy" and help to shed some insight on the psychological catalysts that build natural links.

1. Non-Commercial
   The Internet's Linkerati love non-commercial content, or material that comes from an indirectly commercial site.  It's the reason Wikipedia is more likely to be cited than your ad-sponsored blog and why your ad-sponsored blog will outperform the blog on your e-commerce/affiliate website. Recognizing this pattern, you can take steps in everything from domain name choices to visual design to ad placement to help bolster your "non-commercial" street cred.
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2. Motivated by "Pure" Intentions
   As with "non-commerciality," intent is becoming a bigger part of the link building puzzle. SEO savviness continues to grow, and as it does, greater scrutiny is applied to microsites, linkbait and viral content of all types. Tweet an image on Flickr or Imgur and your intentions must be pure. Point to an image embedded in HTML on your site, and you could just be trawling for links. It's why we have to tell clients and colleagues to "look natural" - 5 years ago, this was barely an issue, but 5 years from now, it will be even worse.
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3. Aesthetically Pleasing
   The visual design of a site and its content is a key part of #1 and #2 above, as well as being its own motivator for linking or leaving. Modern, clean, stunning design works great (see my old post, Yes, Virginia, Design Can Be Linkbait, Too), but so does amateur chrome, so long as the quality is tolerable. The former does so because of its professionalism and credibility, while the latter operates on the psychology of "pure intentions" and "non-commerciality."
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4. Easily Consumable
   I recently wrote about Best Practices for Content Optimization, and these principles apply directly. Make easy-to-read text in usable, scannable formats with pretty graphics and compelling writing. Your link popularity metrics will reap the rewards.
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5. Targeted to a Citation-Likely Audience
   As we know from The Secret to Ranking at the Search Engines (that's really no secret at all), the audience of natural linkers on the web is far different from the standard demographics. Appealing to this group with your content is critical to earning their references - and though they're growing in size and variety, it's still essential to have some effort to reach the core of this group.
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6. Credible
   Material, data, and even opinions that are well-researched and come from a trustworthy, reliable, well-known source are far more likely to be cited than those that can't fulfill these criteria. It's why you'll need to work much harder to get noticed if you're just starting out, than if you've already established your unimpeachable accuracy.
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7. Likely to Trigger an Emotional Hook
   I've covered this in-depth in the past (see The Emotions That Make Us Link). Essentially, certain emotional responses trigger the desire to write about (and reference) certain kinds of content, data, opinions, etc. One of the most brilliant applicants of this logic is Seth Godin, whose blog not only covers short, broad subjects that frequently create an emotional response, but also doesn't allow comments, forcing those who want to provide their opinions to reference his work from their own sites & pages.
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8. Easy to Share
   Yes, people on the web are lazy. Make it easy for them to spread content with copy+paste HTML, short URLs, and social media sharing links and you'll find the ratio of those who spread rises.
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9. Appealing to a Non-Competitive Market
   Perhaps the least known of these tenets, appealing to non-competitive markets is quite intuitive. Let's say you're in the field of real estate, and you write phenomenal content about the real estate market in your city - something every broker and agent will love and want to share. Guess what? They're not going to. They are your competition, and they'd rather staple their eyeballs together than help you rank better for keywords they're targeting. Recognize this, and you can start focusing your content on markets who won't feel threatened to cite your works.
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If you can improve the reference-worthiness of your content, the returns are easy to calculate (though precise measurement is challenging). For every site on the web, an equation like the following exists:

Natural Links Earned / Month = Monthly Visits*Link Conversion Rate

Any increase in the LCR (Link Conversion Rate) produces a proportional increase in the number of links earned. Websites that have figured this out and built strategies to leverage it are going to win on the web. Links aren't just ways to get search engine rankings; they build branding, send direct traffic and inspire social media sharing. If your competition has a higher LCR than you, it's only a matter of time before they lead in market share.

Looking forward to your thoughts and ideas on how to improve LCR.