I use WP Auto Affiliate Links,this plugin gives you the ability to turn keywords into affiliate links automatically
also in this plugin you have the possibility to associate a keyword to a link.
This will help also getting listed in a search engine during a keyword search.
This is very useful because you can automatically interlink your affiliate links with the keywords doing them more visible.
There’s no need to go back through all of your posts by hand and add affiliate links to products related to your content.
You get some other helpful features such as follow/nofollow settings and there’s also a link cloaking setting.