This plugin is better than Nrelated, or Yet another related plugin, etc., as it's much easier to configure -- someone in here mentioned it was confusing. That's simply not the case. Upload it via your WP admin, activate it, adjust the settings .... You get to choose between 7 or 8 different types of layouts, and click save. And it's compatible w/ WP 3.5.1.
So that's it -- simple, and it works just how you want it to work -- and it's lightweight; doesn't hurt your page load times like some others do. I'd recommend this.