cedbv

Don’t Work in WordPress MU. WordPress 3 only. 
Usefull only if you have a multisite install and if some users manages more than one blog.
This plugin adds a simple dropdown menu in administration header that allows you (and every site users) to switch 
between administration of every site they are member of (and so work for super-admin, admin, contributors,…).
Work best if the plugin is Network Activate.

Multisite Switcher

In a multisite configuration, add a dropdown menu in administration to let you switch between sites admin.

sevenspark

The Menu Swapper provides two utilities:
<ol>
<li>
A settings page that allows you to register unlimited menu theme locations
</li>
<li>
A meta box that will appear on Pages and Posts, which will allow you to replace existing menu theme locations with your new theme locations for those individual Posts/Pages.
</li>
</ol>
<a href="http://www.youtube.com/watch?v=kAd0_RKvvLw" rel="nofollow ugc">Video demo</a>

Menu Swapper

The Menu Swapper allows you to register custom theme locations and easily swap menus on individual Pages or Posts.

Multisite Switcher vs Menu Swapper