ABCdatos

In a nutshell: You don’t want robots wasting your resources and slowing down your site if they don’t give you some kind of direct or indirect benefit. An optimal configuration will maximize your SEO results and reduce your operating costs.
You’ll need less than a minute to set your site characteristics and get a customized robots.txt configuration installed, matching your needs and easily updated without headaches. Let us to apply our experience in maintaining and optimizing sites. A clear knowledge of what we want to do and why, moved us to change the decission method from human created robots.txt to an automated system, things are simpler as they seems. Here comes to help this plugin, doing all the magic for you.
Some of your site specs will be automatically detected to reduce the manual config needs to the minimum. A few simple questions about your site will be enough to vast majority of sites.
<h3>Update procedure</h3>
Any change required to the robots.txt is applied in real time when operating in virtual file mode. If you are working in real file mode, after updating the plugin version you should click the Save Changes button in the configuration screen to regenerate the robots.txt file.

Magic robots.txt

This plugin automatically creates a robots.txt analyzing your site to improve your Google ranking and site performance.

sdesalas

This plugin allows WordPress to block over 95% of spam comments using a time-based hash.
This allows for a minimum sanity check and yet should remove almost all spam comments 
without the need to sign up to any third party APIs.
The plugin has been tested in real world conditions for around 12 months. It will not block 
real comments and it is pretty effective against spam, however it only uses a very simple 
algorithm and for that reason some spam comments may still make it through.

WP Simple SpamCheck

This plugin allows WordPress to block over 95% of spam comments using a time-based hash.

Magic robots.txt vs WP Simple SpamCheck