In many online markets, pay per click (PPC) is the fastest way to get customers -- and can readily scale as your budget grows. But sometimes we get too focused on the short term results, and neglect the long term approaches that generate traffic and business over time.
First, make sure that what traffic you do get is used effectively. Make sure that you are genuinely offering value to visitors, and that you work to optimize your site with an ongoing testing program. Make sure that you are capturing contact information from visitors (even if they don't purchase) so that you can develop email based nurturing campaigns, sending offers and information that is relevant to the visitor. You should, of course, make sure that you have permission to send emails.
Public relations can be a great approach for building awareness and value of your site -- make sure your PR activities include respected bloggers and other websites that apply within your market. Customer case studies -- with real customers -- talking about the value of your site and how it helped them are the fundamental building blocks to generating coverage. A key benefit of online PR is that it helps generate more links to your site, which are essential to organic search results.
Partnerships may also be great business development approaches for you. Are there complementary businesses or sites that are of interest to your visitors? Perhaps you and a partner can cross-sell on your sites?
Finally, think about how your existing customers can help spread the word. Make it easy for your satisfied customers to tell a friend -- what if each customer communication included a coupon that could be forwarded to a friend?