Absolutely, positively squash an event in the most cross-browser-compatible way imaginable (thanks, IE8).

killEvent.js

// see http://www.quirksmode.org/js/events_order.html for a fun read
// if you're wondering why all the type-coercion b.s., why not, since this function has to exist in the first place
function killEvent(e) {
  e = e || window.event;
  e.cancelBubble = true;
  e.returnValue = !true;
  return !!(e.stopPropagation && (e.stopPropagation() || e.preventDefault()));
}