RazielKanos

This plguin simply adds a CSS code into your Admin Dashboard and hides most of the nagging messages telling you 
that you should activate or register other GPL 2 Plugins.
It doesn’t add any functions other than adding the CSS code, so there should be no trouble with other plugins you are using.

WP Remove Admin Register Nag

This plugin removes the reminders that you should register plugins you got by a theme for example

Sergey Biryukov

Checks via Google Search if the comment being left is a common spam comment.
Inspired by <a href="http://alexking.org/projects/wordpress" rel="nofollow ugc">Delink Comment Author</a> plugin from Alex King.

Unique Comments

Checks via Google Search if the comment being left is a common spam comment.

WP Remove Admin Register Nag vs Unique Comments