Hey Roger. I tend to use themes that have this feature build in or recommend doing it manually. However, as @christopherM says below, YARP http://wordpress.org/plugins/yet-another-related-posts-plugin/ is often to used to manage this but his caveat that it can put a huge load on a site is worth noting, especially as Google uses site load times as a ranking metric. If you try it out, keep an eye on it with P3 http://wordpress.org/extend/plugins/p3-profiler/ I'd also NEVER recommend it on a siterubix site, I've seen a case where it proved incompatible with a theme and it needed FTP to remove it. Rich.

Great question, would love to know if there is a recommended plugin for this. Don't want to add just any and cause potential problems

I recently started using YARP (yet another related post) plugin. As far as I know that the most popular one. Before that I just linked to my related posts manually. I've heard that YARP and similar plugins can cause your site to be slow, so you might keep that in mind.