Oldie but goodie guide for basic Terminal commands.
Dust-Me Selectors is a Firefox extension that finds unused CSS selectors by inspecting your stylesheet and comparing the rules with the elements in your markup.
A must-have for your webcraft toolbelt.
Version control is a key part of a successful software project, and we use Subversion heavily at Automattic. All our themes, side projects, and even PSD files go into SVN repositories.
We often talk to theme designers that are getting into more advanced theme development who need a quick crash course on using Subversion. As part our tips for version control we recommend keeping a handy reference guide at your fingertips for common Subversion commands.