James Swindle

You can add a reviewed item to any blog post and will display stars at the bottom of said post. Adding this Schema.org markup will show your rating in the Google result and better your search ranking in general.

Review Schema

This plugin will add Schema.org markup options for reviews.

Aaron Queen

There are many sites that are crawling for user-generated reviews now, including Google Places and Google Local Search. WP Customer Reviews allows you to setup a specific page on your blog to receive customer testimonials for your business/service OR to write reviews about a product.
<ul>
<li>WP Multisite and Multiuser (WPMU / WPMS / WordPress MU) compatible.</li>
<li>All submissions are moderated, which means that YOU choose which reviews get shown.</li>
<li>Reviews are displayed to visitors in a friendly format, but search engines see the Schema.org microformat.</li>
<li>Multiple anti-spam measures to prevent automated spambots from submitting reviews.</li>
<li>Completely customizable, including which fields to ask for, require, and show.</li>
<li>Shortcodes available for inserting reviews and review form on any page or widget.</li>
<li>Works with caching plugins and custom themes.</li>
<li>Includes an external stylesheet so you can modify it to better fit your theme.</li>
<li>Reviews can be edited by admin for content and date.</li>
<li>Admin responses can be made and shown under each review.</li>
<li>Support for adding your own custom fields.</li>
<li>The plugin can be used on more than one page, and can be used on posts.</li>
<li>Supports both <code>Business</code> and <code>Product</code> review types.</li>
<li>Shows aggregate reviews microformat.</li>
<li>Fast and lightweight, even including the star rating image. This plugin will not slow down your blog.</li>
<li>Validates as valid XHTML 1.1 (W3C) and valid Microformats (Rich Snippets Testing Tool).</li>
<li>And much more…</li>
</ul>
Almost every new feature that has been added was due to the generous support and suggestions of our users. If you have a suggestion or question, do not hesitate to ask in our forum.
More information at: <a href="https://wordpress.org/plugins/wp-customer-reviews/" rel="ugc">WP Customer Reviews</a>

WP Customer Reviews

Allows your visitors to leave business / product reviews. Testimonials are in Microdata / Microformat and may display star ratings in search results.

Review Schema vs WP Customer Reviews