I have searching so many GPL WordPress Plugin for related posts for my blogs. I was found some tips by adding directly code on the themes, and I was try to search how to add related post ability using some plugins and this is some of my list of Related Posts plugin that available on the net
- Yet Another Related Posts Plugin (YARPP), by mitcho (Michael 芳貴 Erlewine).
- Similar Posts, by Rob Marsh.
- Aizattos Related Posts, by, um, Aizatto, I guess. This plugin no longer seems to be maintained officially, so that link is to an unofficial mirror.
- WordPress Related Posts, by Denis (Hua?).
- Wasabi Related entries plug-in.