Bookmarklets are self-contianed javascript bookmarks that do fancy things to help out with your web browsing.
CSS2: Absolute and Relative Positioning explains how to use absolute and relative positioning to create interesting layout effects.
CSS2: z-index explains how z-index works in order to help you build layered effects with CSS.
The CSS and HTML Slideshow is a neat way of creating a slideshow from a single HTML file. The slideshow is built to be easily styled and is self-contained for easy portability. You can even use data: URIs to package up images for a single-file solution!
In Stateful CSS Mouseovers you'll learn how to leverage CSS2's z-index, positioning and :hover to create fancy stateful mouseover effects.
CSS Mouseover Menu is yet another way of using CSS to create a menu. The technique used is an adaptation of the one presented in Stateful CSS Mouseovers.