Kevin Reid: Web Development

SVG

2003: Animation Test (just animating lots of parts)
2003: Bouncyworm (complex pattern)
2003: Roll (goes somewhere)
2004: Linkage (adjustable)
Note that all of the above rely on SVG animation and will not work with current Firefox and Safari SVG support (as of 2009-06-13).
On Waterpoint, I have implemented a SVG-based ocean map which displays the location of things in the virtual ocean and uses SVG animation to predict future locations.

2007?: Object embedding test. Tests browser support for atypical combinations of media types and embedding elements (e.g. image/gif in OBJECT, image/svg+xml in IMG). Needs some more test cases. (Slightly polished 2009.)
2005: Test cases for your document title fetcher.
2003: Experiments with CSS-based mouseover menus.
2003: The Very Ugly Page. Started out to check browser conformance regarding border-color, now also exercises absolute positioning, :hover, text-transform, overflow: hidden, :first-line, :first-letter, and shows a slightly tweaked-to-look-better drop-cap effect.
2003: Find out what your browser shows for the CSS 'system colors'.