WordPress MU community site by the people at Incsub (professional WPMU developers).
Incsub are a WordPress MU development company. They manage EduBlogs.com amongst others.
Crowd Favorite are WordPress plugin and bespoke site developers. They created an Answers.com AnswersTips plugin.
WP Remix is a highly customisable, commercial WordPress theme. It has various home page layouts, single page layouts, and so on. These can be used in combination to create many different versions of the theme.