itgoldman

This plugin shows on hover sub menus of recent posts, pages and custom post types. 
It’s a simple no-settings out-of-the-box solution for better productivity when using the wordpress admin.

ITG Admin Hover Menus

Shows on hover sub menus of recent posts, pages and custom post types.

yonisink

Create a WordPress menu (up to three levels) with the WP appearances built-in menu builder and convert it to a nice responsive dropdown using template tags.
Choose your colors, and whether you want a hover or click (click will be permanent on responsive break due to mobile devices’ use of hover as a “pre-click”).

Sinking Dropdowns WordPress

Convert default WordPress menu to a responsive hover/click dropdown menu.

ITG Admin Hover Menus vs Sinking Dropdowns WordPress