Link Popularity Building and Increasing PageRank

The theory goes something like this: The search engine powers-that-be, have decided that if other sites are linking to your site, it must be a winner, therefore, it deserves a boost in rankings (when all else is equal). If you think about it, this makes a lot of sense. People link to good sites, not bad ones.
Most search engines are thought to place some emphasis on link popularity in their ranking algorithm. Some people believe that the number of sites pointing to your site is what determines your link popularity, and the more links there are, the higher your ranking will be. However, that is only partially true. The search engines (and those that program them) are not dumb. They are used to search engine spammers trying to cheat their way into getting a high ranking. Because of this, the search engines are not just looking for the number of links that point to a site, but the quality of those links.
Read the rest of my link popularity article for more on why linking is important.
Building Vertical Links

Our vertical linking campaign will help you obtain listings on high-quality sites, which complement your business. Think of it as a partnership of sorts. If you sell shoes, perhaps we'd request links from sites that sell socks. Sell salt? What about those pepper sites? You get the idea.
Link Popularity Building can be used alone or in conjunction with any of the other search engine optimization services we offer. It is highly recommended that this option be purchased along with any full search engine optimization services. Increasing the links to your site will usually increase your rankings within the major search engines.