Using CSS to consistently style forms buttons across IE, Firefox, and Safari.
Nasty Nets used CSS positioning to "embed" one YouTube video into another. "Be sure to hit 'play' on both YouTubes." Reminds me of the animated GIF mashups (more).
New design for A List Apart, the venerable Web design site, done with XHTML/CSS (of course) and Ruby on Rails. (via waxy)
Giant-Ass Image Viewer. Python script (+JavaScript and CSS) for cutting up and viewing large images, a la Google Maps.

