Cross Post plugin for WordPress MU. Allows a post to appear in multiple blogs.

Allow a user to author a post accross multiple blogs in the same Multi-Site install.

WordPress to Posterous plugin.

Increase your Visibility and Blog Traffic. This plugin allows you to write a WordPress blog and cross-post it to your blog at BestThinking.com.

Auto publish your new and old blog content to Social Networks. Auto post to Twitter, Facebook, Linkedin, Pinterest, Blogger, Tumblr..