A good business directory has to do something other than stock installable business directory or web directory scripts.
In short, it must be outstanding and unique, not simply in look, but in one predominant factor. That is, encouraging interactivity.
A lot of directories out there are simply lifeless binary matter, existing merely to give you a link to your site, nothing more.
But anyone who knows a grain about SEO knows that these are not the main ingredients for traffic. Google has of late updated its ranking mechanisms to increasingly phase out backlinking as a sole determinant of page authority. Yes, pagerank is a factor, but a factor among 200 other factors. And a link is a link is a link is not true. Beyond implementing no-follow standards to differentiate links, Google does assign certain authority to certain referrals above others. Doing a backlink analysis of a top keyword will often show certain sites that have few links ranking with those websites that have thousands and thousands of backlinks. How do those small unknowns rank among the "majors" if not because of Google's algorithm prizing link quality, good neighborhoods and on page SEO factors above dead directory referrals.
What is important is that you find a living and breathing directory, one that provides free business directory listings is welcome, but above this fact, it should provide a basis for interactivity. Social media, when separated from the buzz factor that word pairing sets off, means communication. It means networking for businesses. It means life, which is important to business and creates a two prong referral for your business, both by driving directory based traffic and inquiries and in increasing your value for search based inquiries as search mechanisms like Google evolve to become higher order cognitive determiners of life and activity rather than simple statistical counters.