Ariana

This is a very simple plugin that adds a “robots” meta tag to the head of your site with “noindex” in it.
The effect of the noindex robots meta tag is that search engines will not index your pages and posts at all. 
This is a better solution then the wordpress default settings option, which tells search engines to not crawl the URLs in the robots.txt. Because Google (and other search engines) sometimes still index URLs they haven’t crawled, for which they determine relevancy based on anchor text of links which lead to the specific URL.

Simple Noindex

Eugen Bobrowski

Plugin provide to help search engines to indexing site correctly.
A simple plugin to manage your robots.txt. Plugin donn’t create the file or edit it. This plugin edit WordPress output of robots.txt content. And get you a easy and usable interface to manage it.
Features
<ul>
<li>Drag-n-drop robots.txt paths</li>
<li>Changing <code>blog_public</code> option form plugin settings page</li>
<li>Site map field for robots.txt</li>
<li>Robots.txt physical file checking.</li>
</ul>

Robots.txt rewrite

first review

Provide the easy managment of your robots.txt from admin side. It propose you the advanced then standard robots.txt content too.

Simple Noindex vs Robots.txt rewrite