and (I believe) 99% of the references you'll find will be people trying to get you to pay for it, and they'll offer little benefit or maybe even harm your site's ranking on various search engines.
Something else that can boost your ranking is to have sites that cover the same topics as your site link to your site (the more that link to you the more that your site is seen as a primary influence for that topic). Please note that this should be done on a genuine relationship basis as contacting multiple sites and saying "please link me!" will not get you anywhere and make you even fewer friends .