Link building is a major element of Search Engine Optimisation. It is a means of increasing 'pagerank' but only if done correctly, and using effective and relevant sites.
Basically, if you manage to get a link on a site with a greater pagerank than the page on your site that it links to then some of their rank rubs off on you! There are certain points that should be noted about link building...
1] Don't add too many too quickly, search engines see it as spam!
2] Be selective in what sites you link from.
3] Where possible place a keyword rich 'deep' link to a page within your site rather than the homepage itself.
4] Keep track of what links you have placed where, and maintain them (if for example you alter your site, don't leave a dead link on the linking site!)
Over time I have gathered various hints and tips for link building, and I am in the middle of implementing my own campaign. Link renting does exist, but in my opinion unless the price is right, the site has a good pagerank and their content is relevant to your site - I am not a big fan.
There are some paid directory listing that would be worth a look if you have some cash burning a hole in your pocket - Yahoo! ($299/year with a PR8), Best of the Web ($200 with a PR7) and a more affordable Clush ($20/year and a PR7).
This is a service that I offer as part of my
web marketing services, (what a perfect example of a deep link that didn't cost me the earth!)
Regards,
Gordon