Some open source projects that were used in the making of this site:
Bootstrap from Twitter: Completely essential to the front end of this site. Each major part of the UI, including toolbar, form elements, modal windows, alert messages, and the layout grid itself are borrowed from the Bootstrap CSS toolkit.
Even though my background is in design (and maybe because my background is in design, I like to code some functionality first before I start making things look better. With Bootstrap, I could attach one CSS file and have a baseline typography and grid system that made it all the way through to the final product. (It's also easy to customize on top of Bootstrap, and I added lots of CSS3, @font-face and other goodness without any trouble.)
LESS CSS: You've probably heard of what LESS does by now (nest styles, use CSS variables, etc.) but I was never comfortable with the idea of using less.js to parse the .less file into standard CSS.
Enter LESS PHP. Tell LESS PHP the location of your .less file and the location of your .css file. When you visit a page on your site, LESS PHP compares the timestamps on the two files. If the .less file is newer than the .css file, it will parse the .less and save it as a new .css file. If not, it does nothing. In other words, LESS PHP only gets involved when you've made a change, and it never wastes processing time on the server or in the browser.