I recently put up a related content block on this site and here is how I did it. There are a number of Drupal modules, at least four, for this but a simple block PHP snippet suited me best. This PHP snippet makes sure we are viewing a node.
Drupals “Read more” link is by default displayed together with other links like “Add new comment” at the bottom of the teaser display. Readers not used to blogs and other moderns web sites can easily miss that there is more to read.