Simple Drop Down Menu
55
This clean-looking menu is very simple to implement and can be placed anywhere on a page. Adding or deleting levels is easy to do. The menu is created without tables, using unordered lists and hidden layers.
Expanding Menu
36
This is a simple expanding menu. The anchor tags that expand each menu are added by JavaScript, so the HTML code doesn't contain any event handlers or unnecessary HTML tags. The structure of the menu is defined with unordered and ordered lists elements.
Slashdot's Menu
21
This is a stylish collapsible menu modelled after the navigational menu found on Slashdot. Session-only cookies are used to remember the menu state (whether it's expanded or not). Cool!

New: You can now add a expand/ contract all links to the menu, to allow your visitors to easily toggle the visibility of all submenus. Furthermore, you can specify if all submenus should be contracted by default when the menu first loads (see top of "menu.js").
Drop down menu w/ description
20
This is your straightforward drop down menu, except in IE5+ and NS6+, a description of each selection is displayed beneath it. Very nice addition to a popular application wouldn't you say? Script updated to support options opening in a new window (IE5/NS6+ only), and ability to include multiple menus on the same page.
Tabs Menu onmouseover
16
This is a mouseover tabs menu. Move the mouse over designated links, and additional 'sub links' appear beneath it. Think of it as an inline two level menu. We intentionally made this script with a minimum amount of styling, so you can personalize its look yourself. As an example, the main links could be substituted with 'tab' images instead.
xCollapsible & xMenu5
16
xCollapsible toggles an element's 'display' property when a 'trigger' element is clicked. This behavior is applied to all of the element's nested elements. It works with 2 different HTML structures. The first demo is made of nested ULs, and the second is made of nested DIVs with an H element preceding each DIV (I use this on some of the main pages of my site). Only the outermost UL (or DIV) needs an ID.

xMenu5 is an experimental version of xCollapsible with more features.
SubMenus onMouseover
14
This script will display the submenus when visitors move mouse over the parent menus.
Drop Down Tab Menu
14
This is a lean CSS tab menu that supports a 2nd level drop down menu for any of its tabs. Both the tabs and the drop down menus are implemented as plain HTML for easy modification and search engine friendliness. A close relative of Chrome CSS menu
3-State highlight menu effect
9
This is a 3 state menu effect, applicable to any table. The table cell in question 'hovers up' when the mouse moves over it, and depresses when down. A snap to install, your table links will never be the same in IE4+ and NS6!
dhtmlxTabBar
8
dhtmlxTabBar Standard Samples.
Animated MiniTabs
8
A sleek animation effect using tabs for a slide navigation bar. Degrades very nicely when JavaScript is turned-off.
Omni Slide Menu
8
Omni Slide Menu is an super versatile slideout menu that reacts to the mouse hovering over and out of it. It supports enough features to make your head roll, though the default setup only takes a second to implement. All settings to the menu is done inside an external .js file.
Chrome CSS Drop Down Menu
7
We decided to create this script when we needed a compact CSS drop down menu for a project. Chrome Menu is a CSS and JavaScript hybrid drop down menu. It's easy to configure and search engine friendly. The menu links is based on a list, while the drop down menus are simply regular DIV tags on page. Thanks to JavaScript, the menu supports subtle but important effects such as delay before menu disappearance, and repositioning of the menu if too close to any one of the four corners of the window. The entire menu, including images and external files, is extremely compact, at around 6 kilobytes.
2 level Horizontal Tab Menu
7
A CSS based tab menu that supports a secondary level of menu items. Both levels are horizontal, so there no drop down menus that may become hidden underneath form elements in browsers such as IE. Cool!
Unobtrusive JavaScript Image Rollovers
7
Create image rollovers for your navigation without hardcoding any JavaScript into the HTML code on your Web pages. Easy to implement, even for beginners, and works across all browsers. Degrades nicely for visitors with JavaScript turned off.