This Related Posts Plugin for WordPress displays links to a given number of Posts that are related to the current post(s) by Tags or Categories. It can Automatically add links to Related Posts at the bottom of every Post or you can drop the Widget on your sidebar.
Settings: Excluding posts, categories, and tags; section heading; number of links; display post date; and excerpts.

EZ Related Posts Footer Links and Widget

Display a linked list of related Posts by Tags or Categories at the bottom of every post or on the sidebar. Options to show Post Date and Excerpts.

Gerasimos Tsiamalos

Anastis Sourgoutsidis

Most of the “related posts” plugins out there while they provide some kind of control on how to create related posts, they all rely on an algorithm 
and the results are automatic. With CPTR you get total control as you can manually select the posts that you want to relate.

Custom Post Types Relationships (CPTR)

This plugin will let you create custom post relationships among posts, pages and custom post types.

EZ Related Posts Footer Links and Widget vs Custom Post Types Relationships (CPTR)