As recommended by Typepad here, I have installed the LinkWithin Widget which says it indexes your blog, finds related posts and provides links at the bottom of the post.
Certainly it does provide links, and even picks up an image from the post to show, which is rather good. Users claim it significantly increases pageviews. But its idea of what is a related post is rather bizarre. You would think it would use the tags I put on each post rather than guess. I've left it installed for humour rather than usefulness.
Feel free to leave a comment on any page, about the appropriateness of what it suggests is related.