Roy Tanck

This plugin will help you:
<ol>
<li>Find plugins and themes that are not active on any blog.</li>
<li>Determine the impact in case a theme/plugin needs to be upgraded, removed or reconfigured.</li>
<li>See if a widget is in use on any blogs, and track down where.</li>
<li>Find users who do not have a role on any site (and are not network administrators).</li>
</ol>
This plugin currently does nothing on single-site WordPress installs.

Network Admin Assistant

Helps you manage a WordPress network by displaying useful statistics.

Aaron Axelsen

The Multisite Administration Tools plugin adds additional columns to the Sites, Plugins and Themes tables in the Network Admin interface.
On the Sites table, two additional columns are added to allow admins to easily view the theme of the site, and also any plugins that are enabled.
On the Themes table, there is an additional column added which allows the administrator to see all sites that are actively using that theme.
On the Plugins table, there is an additional column added which allows the administrator to see all sites that are actively using that plugin.

Multisite Administration Tools

Adds information to the network admin sites, plugins and themes page. Allows you to easily see what theme and plugins are enabled on a site.

Network Admin Assistant vs Multisite Administration Tools