I've developed a new wordpress plugin that will help you add affiliate links automatically in your content. The plugin is called WP Auto Affiliate Links How it works: After installing go to "Manage Affiliate Links" in settings menu and start add your affiliate links along with keywords or keyphrases where you want the links to be added. The plugin will search the content for the keywords you enter and will add the affiliate links over them. You can get the plugin here: http://wordpress.org/extend/plugins/wp-auto-affiliate-links/ The plugin is still in a development phase so any suggestions or bug reports are welcome. I am still working to add new features to it.
A major update has been made for the plugin, many problems resolved with the replaced words. Version 0.1.7 is out: http://wordpress.org/extend/plugins/wp-auto-affiliate-links/
After months of development, the plugin reached the 2.2.3 version, which is stable and can be widely used. Here you can download from wordpress plugin directory: http://wordpress.org/extend/plugins/wp-auto-affiliate-links/