Plugins/Styles

CSS Switcher: This plugin really isn't a plugin. There are only a couple of files to download. You just download the zip and do what the instructions say. It can't break because I built it using standard HTML.
Filosofo Highlight Current Category: Add a class to the category link to highlight the category under which you're currently browsing the archives. Works in WordPress 1.5 and newer, including 2.0.
Per-Post Styles: Define stylesheets specific to an individual post or several posts using custom fields as well define stylesheets for the posts of an author (control backgrounds, colors, font-sizes, variants).
Post Templates by Category: Set a custom template for all posts within a category.
StyleSheet Chooser: Allows the visitor to choose between various stylesheets and remembers that choice using cookies.
Sweet Titles: Implements Dustin Diaz' Sweet Titles onto your blog.
ThemeSwitcher: Theme Switcher allows your readers to switch among installed themes.
Cross-theme Stylesheets: Adds links or imports to the head for user-defined stylesheets. These stylesheets are independent of the chosen theme and are managed entirely from the control panel. The sheets can be linked to whatever set of media you choose. Needs WP 1.5