This plugin makes it super easy to manually select related posts. You can search and select posts that fit your criteria, all from within the write/edit post screen.

Avert successful hacker attacks and enhance security with this easy-to-use plugi

Manage your Ads, Control Who Sees Them

This plugin adds voting functionality for posts. This function is similar to Reddit or Digg, in that visitors can vote for and against. Votes for the post will fill up the bar (in blue), while votes against the post will empty the bar.

Have your browser understand what you are blogging about and suggest pictures, links, articles and tags to make your posts more vibrant. Sounds interesting but I'll wait for it to get out of alpha.