WP Plugin: ClassyBody Add a class to the body tag of your WordPress blog depending on various parameters such as single page, page, post, category etc. In other words, it gives you the power to control the look and feel of your blog using CSS but dependent on the condition of your blog that your visitor is viewing. You could make your single pages look different or a single post have a festive theme with modification of the CSS.
Reminds me of some functionality found in the Sandbox (and now K2 and perhaps others) theme.