agrafix

This plugin adds hyperlinks to specified words in posts and pages. This can be very usefull if you are using complicated words and want to link Wikipedia articles or 
if you just want to improve your seo by linking some interessting words 🙂
<h3>Example</h3>
Your Text: 
 Welcome to a blog about google
Your Plugin-Settings: 
 blog|Wordpress software|http://wordpress.com 
 google|Search engine|http://google.com
Result: 
 Welcome to a <a href="http://wordpress.com" title="Wordpress software" rel="nofollow ugc">blog</a> about <a href="http://google.com" title="Search engine" rel="nofollow ugc">google</a>

agLinker

This plugin adds links to specified words in posts and pages.

Phil McDonnell

WP Categories and Posts is an extension of the core WordPress function called <code>wp_list_categories</code>. This plugin adds in a template tag you can use to display categories and sub categories and the posts underneath those categories.

WP Categories and Posts

This plugin adds in a template tag you can use to display categories and sub categories and the posts underneath those categories.

agLinker vs WP Categories and Posts