Multisite blogging question

I have a main site and bunch of other mini sites which were created using the multisite ability.

Example

Main site: Home
Mini sites: IT, Marketing, HR

How would I get the blog posts from the mini sites to all show up on the main home site similar to a compiled newsfeed. I want all the most recent posts to be all in 1 list and have the name of the department/mini site as the author.

Anyone worked with this before?

I want a dynamic sidebar where the blogs come in automatically and the main container will be static.