Dynamic CSS

simplebits.com has an interesting feature that allows you to toggle the site from fixed width to fluid very easily. this could easily be used for other things as well, such as raising the font size, color scheme... really anything that's in the CSS.

www.simplebits.com/notebook/2006/04/24/toggle.html

also, i really like this site because of the girls it is an excellent example of what AJAX can do.