Here are some WordPress plus plugins you can use to put Amazon ads on your website. I also included the pr(page rank) of their plugin home pages so you can help gauge their quality.

Amazon WordPress Plugins

1. Amazon Link pr5 -  Provides a facility to insert Amazon product links directly into your site's Pages, Posts and Widgets and Templates.
2. Amazon Widgets Shortcodes pr4 - Keep your time and save your money with these Amazon widgets shortcodes. Standard compliants, easy to use and so on !
3. Amazon Affiliate Link Localizer pr4 - This plugin automatically changes your Amazon links to point to your visitor's local Amazon store whilst using your affiliate ID for that country
4. Amazon Product In a Post Plugin pr3 - Quickly add formatted Amazon Products to post/page by using just the Amazon ASIN (ISBN-10). Great for monetizing your posts.
5. WordPress Amazon Associates pr3 - Quickly and easily monetize your website with links and widgets from the web's top Affiliate Program, Amazon Associates.
6. Ad Inserter pr3 - Integrate any HTML code into WordPress. Just paste the code and select the location and display mode. Perfect for AdSense or contextual Amazon ads.