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.

jonkemp

Adds the noindex meta tag to your WordPress Login page.
If your WordPress blog has a public login page, you probably don’t want it to be indexed by search engines. Noindex Login adds the robots “noindex” meta tag to your login page to keep search engines from indexing it. It also works on your registration and lost password pages.

Noindex Login

Adds the noindex meta tag to your WordPress Login page. If your WordPress blog has a public login page, you probably don't want it to be indexed …

Better noindex vs Noindex Login