UberMenu or the WordPress Mega Menu plugin is probably the best drop down menu plugin for WordPress.
UberMenu plugin lets you create great drop down menu in WordPress, where you can add virtually anything in the drop down. You can add thumbnails or icons, maps, contact form, search form and even a gallery to the drop down menu box.
UberMenu plugin integrates seamlessly with the WordPress 3+ nav menu system (Appearance > Menu). It helps you style your navigation menu easily using its style generator. Multiple predefined styles are already included with the plugin so that you can use it out of the box with an existing style.
Video: How To Create a Mega Menu Easily Using UberMenu Plugin
Overall UberMenu is the best plugin to create awesome drop down menus for WordPress that we have ever encountered. Check out UberMenu now.