The ARI YUI Menu module is the best I've found. Very reliable and easy to install. I'm a developer, programmer and joomla installation pro. I installed mod_ariyuimenu, version 1.0.4 three days ago on a clients site that needs many different menus throughout the site with reliable dropdown menus both horizontal and vertical in layout. I've used almost every high rated menu extension and tested in all browsers. This module is the most compatible with all of them. It's also very easy and logical to style in the safe_menu.css stylesheet located in the modules>mod_ariyuimenu directory js>build>menu>assets>skins>sam directory. There is a problem with IE 7 positioning the dropdown correctly -- but easily fixed by using css positioning.
One thing I needed was to over ride some styles (different in different menu's) but I just noticed ARI Soft has updated to a new version 1.0.5 that has a CSS Styles override in the module parameters section. I'll upgrade and try that.