Mark Ghosh have upgraded and consolidated his old Contextual Related Posts Plugin for WordPress. This new version (1.1) is a simple install (just install the plugin file) and it will show the last 5 related posts from your blog. The display show the links right after the comment form. The matching is done with the post title of the post being viewed. Examples include my Retail Junction (WordPress 2.0) and Sap-Tricks (WordPress 2.0)
PS: Some theme authors tend to remove default actions from their themes. If you are having problems displaying the related posts, please check with your theme author or post a comment here for help.
Please post bugs and comments.