This dropdown menu uses no javascript and uses valid css and html without the need for conditional comments and without the need for any hacks at all. The drop downs are removed from the flow and will overlap following content such as this.
This is an experimental layout specially provided for my CSS quizzes at Sitepoint and is not meant to be anthng more than an example of what css can do. The code is not very semantic in this example but the techniques used could be used semantically for similar layouts.
The links can be tabbed via the keyboard but the effect is rather strange
Works in IE5 - 8, Firefox 3, Safari 3 - Doesn't work in Opera