Suckerfish Dropdown is a dropdown menu built with CSS with a little bit of JavaScript bolted on to accommodate Internet Explorer, which doesn't support the :hover pseudo-class on anything other than links.

The original method was already lightweight, accessible and cross-compatible, but this method is even more so. It now works with multiple-level dropdowns, the JavaScript that mimics the :hover pseudo-class is just 12 lines long, to improve accessibility display: none is no longer used and problems that were encountered with Opera and Safari browsers have been overcome.
Son of Suckerfish Dropdowns