These are few best plugins list which can be useful in wordpress MU Blog:
– User Themes: It will provide functrionality for system administrators to move themes to users file folders and allowing them to edit their themes.This feature is managed via Site Admin
– WPMU Sitewide Feed: It generates three RSS 2.0 feeds comprising of posts, comments, and pages across all blogs on WPMU powered site.
– Anarchy Media Player 2.0: Anarchy Media Player 2.0 for WordPressMu will play any simple href link to mp3, flv, Quicktime mov, mp4, m4v, m4a, m4b, 3gp as well as Windows wmv, avi and asf files, in the appropriate player on your web page.
– Sidebar Author Registration: Adds a sidebar widget for users to auto-register as authors. Drop in mu-plugins. Then add the widget to sidebar.
– List All Widgets: Adds sidebar widgets to let you display new/updated/active blogs from WordPressMU.
– Change Blog URL: It allows blog user to change their blog URL from existing one. The admin page can be access at Option->Publishing.
– List All Blogs: Lists all blogs on a WPMU site. Simply place list-all.php in mu-plugins directory and then call the list from any page.
– List All Posts: It allows you to place a list of the latest posts wherever you wish.
– Plugin Manager: Manage global plugin policies or just turn on and off plugins for individual blogs.
– Primary Blog Switcher: It will Place a drop down on the profile page to allow a user to select their primary blog. Very useful if numerous blogs on a WPMU system and want default login to be one other than the first blog created.