http://wordpress.org/extend/plugins/plugin-visibility-manager/
The Plugin Visibility Manager for WordPress adds granular administrative control over which plugins are visible in the plugins menu for any given site. Plugins can be made hidden or visible on a blog by blog basis (through the plugins menu) or on a site-wide basis through the ‘Plugin Visibility Manager’ page in the Super Admin menu.
Plugins can be active even if they are invisible, but this can only be controlled by Super Admins. Blog administrators only have control over visible plugins.
The Plugin Visibility Manager automatically makes itself invisible. It also makes the Theme Visibility Manager invisible if it is installed.