multisite advertising and themes

All – I am in the midst of creating my multisite network that will allow anyone to set up their own blog.

I am looking for some feedback or references to learn more about how to implement advertising across the site. Specifically, I want to show advertising, but I am a little confused how a super admin can globally control the ads. Are there plugins available? Or will I have to go into each theme and set the ads?

Thanks in advance…