ADxMenu is a JavaScript and CSS drop-down menu solution which web designers will find easy to modify.

It supports unlimited sub-menus and offers a simplified usage as it uses the well-known <ul> <li> tags to create the menus rather than JavaScript configurations (JavaScript editing can be done for extra modification).

ADxMenu works in most of the modern browsers (an extra solution exists for IE6) and supports both horizontal & vertical menu types, even right-to-left and bottom-to-top.

woork, a blog that has some very nice web resources, shows how to create the famous digg-like navigation with a tutorial & source files.

The tutorial also explains how to create liquid & rounded corner items that you may find useful.