These are partnership programs that pay affiliated sites by commission. Often, this form of marketing is referred to as CPA (cost-per-action). In order to receive revenue, a site must not only display ads (often with the ability to choose between banners and text links), and generate click-through, but must then generate sales as well. Still, sites offering these types of programs generally compensate affiliate sites at a rate that reflects the hard work that must go into generating a sale.

These programs are best to use when the products on offer are of interest to your site's target audience (ie CD sales at a band fan site or photographic book sales at a photography site), and when they are effectively integrated within the content of your site.

In fact, that is the most positive attribute possessed by affiliate programs. Since you must generate guaranteed sales in order to receive revenue, sites offering these programs usually offer host sites the freedom to link to the site as they wish - through banners, text links, search engines, whatever! (with the exception of mass unsolicited email postings - thankfully). This may enable you to establish a 'giftshop' of sorts within your site, or to place links within the text of an article or movie review. The potential variations are limitless. In many cases, one can also place click-through or impression-based ads on the same page at which commission-based text links appear (check each specific agencies terms and conditions to ensure that this doesn't breach any contractual agreement).

The pages linked below will direct you towards some of the best and longest-running affiliate programs on the Web: