radgh

This simple and lightweight plugin adds a “Hide from search engines” checkbox above the publish box to pages. By 
ticking this box, a meta tag will be placed into the <code><head></code> section of your page specifying that robots should 
not index the page.
By default this only applies to pages. You may extend this functionality to posts or other custom post types with a small bit of code. See the FAQ’s tab for further instructions.

Noindex Pages

Ask search engines not to index individual pages by checking an option in the publish post box.

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 …

Noindex Pages vs Noindex Login