AffiLinker Affiliate is a free WordPress plugin (also offers a premium version), it helps you to monetize your website by converting your keywords to Search Engine Friendly Affiliate Links automatically. It saves your time and leaves no traces of affiliate links in your source code.
Install and activate it then start adding your new link and keywords. You just have to fill the link (not only affiliate but any) and keywords separated by commas, see following image:
See more of its screenshots for the options of cloud widget, managing links, tracking clicks on each and every Affiliate Link etc.
Example of sample links created using AffiLinker: