What is a Yahoo directory listing but a paid text link!
Ok by Google because of the “editorial review”
Brokers like Text-Link-Ads.com and can help
“ Selling links muddies the quality of the web and makes it harder for many search engines (not just Google) to return relevant results. The rel=nofollow attribute is the correct answer: any site can sell links, but a search engine will be able to tell that the source site is not vouching for the destination page” -- Matt Cutts, Google engineer
Google discounts the voting power of sites that it knows are selling text links:
“… parts of perl.com, xml.com, etc. have not been trusted in terms of linkage for months and months. Remember that just because a site shows up for a “link:” command on Google does not mean that it passes PageRank, reputation, or anchortext” -- Matt Cutts, Google engineer