A lot of Web 2.0 designs these days sport alternating colored horizontal rules, used as either section dividers or element borders. Use this tool to easily generate your own "Ribbon Rules" using random shades of a single color, or explicit colors of your choice!
Below is a sample CSS that runs your ribbon across the top of the page (see top of this page):
background: white url(ribbon.gif) top left repeat-x;
There are countless other ways to utilize the ribbon of course.