That menu is called a "Float Drop Menu" and it uses a 1px change on the float margins to force the sublist into view. It really only works with fixed widths though but works well if you are able to use fixed widths.
It was developed by one of the members here at SitePoint and it was featured as CSS Quiz #27 a while back.
You can learn more about it here at Timo's Site.
The Suckerfish dropdown simply uses li:hover to change the location (either by margins or positioning) of the absolute positioned sublist.