Network Plugin Auditor
As my wordpress network grew I found it challenging to track which plugins were used on which sites as the only way to check was to visit each dashboard one at a time. What a hassle!
This plugin adds a column to your network admin to show which sites have each plugin active (on the plugin page), and which plugins are active on each site (on the sites page). Now you can easily determine which plugins are used on your network sites and which can be safely removed.
Multisite only.
Question? Comments? Check out the Network Plugin Auditor forums threads on WordPress.org