MaximeB

This plugin will check if there are some hidden meta tags with noindex and warns the author of the article. The warning is only visible for the author of the post, or the admin(s).
Features :
<ul>
<li>Check the content of a post and detect the presence of meta tags with robots/noindex in it.</li>
</ul>

Better noindex

Warns the author or admin in case of <meta name="robots" content="noindex"> hidden in a post.

Badi Jones

Duplicate Content Cure is an extremely simple plugin that makes WordPress more Search Engine 
friendly (And therefore improving SEO). It does this by preventing search engine spiders/bots 
from accessing pages like Archives, Tags, and Categories, which tend to contain duplicated content 
from elsewhere on your site. This is achieved by adding nofollow, noindex to 
these problem pages.
Duplicate Content Cure doesn’t have a lot of features that other SEO plugins have, but 
it also is lightning fast by comparison.

Duplicate Content Cure

Duplicate content cure is a simple plugin that improves SEO by preventing search engines from indexing pages that contain duplicate content.

Better noindex vs Duplicate Content Cure