Dustin Diaz’s [getElementsByClass](http://www.dustindiaz.com/getelementsbyclass/) Javascript function is a swell piece of work. Not only will it find all the elements of a given class on a page, but you can tell it to look only in a certain node (it defaults to `document`) and only for certain tags (it defaults to `*`). Be sure to also take a look at [Top 10 custom JavaScript functions of all time](http://www.dustindiaz.com/top-ten-javascript/).