I've been playing around with all the new stuff in HTML and CSS, and a bit with JavaScript. Here are some results. All of them work perfectly in Mozilla 0.9.6, but some will probably break in other browsers.
TIME-magazine-style pullquotes with CSS.
Another pullquote style with CSS, taken originally from a 1996 Wired magazine, which I think is better suited to the Web.
Beveled edges with CSS.
Non-nested boxes around text with CSS, inspired by Wired's calendar format. I added a little bit of dynamicism with JavaScript.
Following the mouse with JavaScript and CSS. I wrote this to prepare for the Breakout example below.
Breakout in HTML with CSS and JavaScript. Not finished.
Text flowing around a circle, or at least an ellipse, with CSS. (You could make it a real circle.)
Drop shadows with CSS.
A fixed background with CSS. Trivial effect, but cool.
A window on a fixed background with CSS.
A table inline in a paragraph with CSS. Renders incorrectly in Mozilla 0.9.6, although it "works".
A JavaScript REPL with a sort of "terminal" look to it. History persistence and cls are broken; the former because I haven't bothered to relearn about cookies in JavaScript.
Option groups got added in HTML 4. I didn't know about them, but they're pretty nifty.