DHTML Menus are those menus that sites use for navigation. They look like straightforward menus at first, but when you click on them or mouse over them additional information pops out below or beside the menu. These menus are great space savers for complicated websites, but they are hard to build. These DHTML menu systems will build them for you or give you a program to build and maintain your own.

Screen shot courtesy Extend StudioFlexiMenusJS is a JavaScript menu builder Dreamweaver extension. If you have Dreamweaver CS3 or CS4, and you want to build dynamic JavaScript menus, this extension makes it easy. There are 15 skins with multiple colors per skin as well as 30 transition effects. Plus you can use your own images and HTML to create your menu items to make it even more flexible. If your site needs menus to be populated from a database or uses server-side languages, then you should get the developer version. Otherwise, the designer version will work fine for most people.
This DHTML menu system has a lot of great features and pre-built menus. Chances are, if you're looking to integrate a menu into your site, you'll find one of the skins already built that would meet your needs with very little tweaking. There is a draggable feature to make the menus draggable on the screen. Or you can set a menu to remain on screen as the customer scrolls. There are a lot of configurable options and ways to style the menu. For the money, this product offers the best value - even if you're from the US with a falling $. This menu system has had massive improvements since the first time I reviewed it. It's great to see companies taking the time to update products and meet customer needs.
DHTML Menu Builder is a Windows application that will build fancy DHTML menus for your website. It supports adding JavaScript inside the menu fields and adding form elements to the fields. It also will validate the links in your menus, so you can be sure that your menus aren't contributing to linkrot on your site.
This menu system has so many options, you could spend hours just playing with your menus. One feature I like is the tuner (a desktop application in Windows or a Web page for Macintosh). The tuner sets all the options and delivers the JS script to upload to your site. There are hundreds of effects and skins to use or you can set your own CSS.
Dynarch Menu is a well thought out DHTML menuing system for a site. It has a lot of features and skins pre-built so you don't have to think about how you might build your menu. Plus, you can use it for context menus and application toolbars and so much more.
SmartMenus is a DHTML menu that is also accessible and SEO friendly. It offers features like a timeout or delay in opening and closing menus, right-to-left and bottom-to-top opening of menus, and a feature to keep the menus inside the browser window.
CSS Quick Menu offers a lot of features including tons of configuration options. It has an online configurator to create both the script and the CSS styles to integrate the menu into your design. I love that it builds 100% valid XHTML menus that don't interfere with the validation of the rest of your document. There are also a bunch of add-ons to enhance the functionality of the menus.
There are literally hundreds of pre-built skins for this menu builder. While the builder is for Windows specifically, there are also plugins for Dreamweaver, Expression Web, and FrontPage. And you can build as many menus for as many sites as you like once you've paid for the program.
This is an elegant DHTML menu that has the added benefit of being free. There are a lot of options you can choose from, and it's easy to install and use.
No free download available, so all information is based on the website. Hiermenus offers good features for a menuing system, but the lack of a free download to try it out before you buy makes it problematic for most users.