Avendi Media

Menu Tamer adds collapse/expand links to nav menu items in the WordPress admin interface. If you have a large navigation menu, managing it can become a frustrating task due to the sheer size it takes up. Menu Tamer lets you collapse any branch of a nav menu to get it out of the way.
Menu Tamer has been tested in the latest versions of Chrome, Safari, and Firefox, as well as Internet Explorer 7, 8, and 9 (understandably, it is much slower in IE, but it works).

Menu Tamer

Adds collapse/expand links to menu items to de-clutter the nav menu interface

joe_bopper

Adds search box as a choice of item in navigation menus admin area.
Features include:
<ul>
<li>now compatible with the WordPress appearance customizer,</li>
<li>search box available as a choice in the admin area for navigation menus,</li>
<li>as many boxes can be added to a nav menu as one likes,</li>
<li>search boxes can be added as children of other menu items (useful for, e.g., mega-menus),</li>
<li>capacity to change button text, placeholder and css classes from the admin area to each search box,</li>
<li>hooks to modify output (see FAQ and/or code comments),</li>
<li>very lightweight,</li>
<li>in keeping styles, html, behaviour, etc., with wordpress defaults,</li>
<li>works straight out of the box, no configuration needed.</li>
</ul>
<h4>Those wanting to translate this plugin, please do.</h4>
I believe the plugin is in a translatable state and I’ll do everything I can to help in translation. It should be relatively quick as there isn’t much text to the plugin.

Bop Search Box Item Type For Nav Menus

I like the way it behaves like any menu item so you can position and decorate it how you want. Thanks to Joe for putting me right on how to get at the placeholder text.

Nice Plugin

Adds search box as a choice of item in navigation menus admin area.

Menu Tamer vs Bop Search Box Item Type For Nav Menus