CodeFlavors floating menu
Create animated navigation menus on the left or right side of any WordPress blog.
Plugin Tag: drop down menu
AllWebMenus WordPress Menu Plugin
Requires commercial (paid) software: AllWebMenus PRO (v5.3.926+)
MenuMaker Lite
MenuMaker Lite provides and easy way to create responsive drop down, flyout, and accordion menus.
Dropdown Menu
Highly customizable automatic pages, categories or custom dropdown navigation menu widget with nice jQuery effects.