Hiding images for Responsive Design
This is probably the most efficient way of hiding an image for responsive design. Tim Kadlec recently did some excellent work testing a variety of browsers and their capacity to download assets specified by media queries.
IE6-8 Box Shadow
This tutorial uncovers a superb technique for CSS3 box-shadow in IE6-8. (The above is actually an image. Visit User Agent Man to see the CSS version)
CSS Lion Notification
Some excellent techniques to take away and incorporate into your next design.
Equal Width Inputs
Fluid Squares V2
A HTML5 fluid grid whose units remain square