Tom Armitage of Infovore has built a CSS Redundancy Checker that will scan a CSS file for selectors that are not used by any HTML files in a specified directory or URI.
The tool can come in handy when you're maintaining legacy sites with countless selectors whose purpose is long forgotten.
The Ruby source files are hosted at Google Code and Mike Malone has put together an online version based on Tom's code so you can run the tool without installing it locally.
"Yet Another Multicolumn Layout" (YAML) is an XHTML/CSS framework for creating CSS-based float layouts.