Monetize like crazy for non-logged in users. Big ugly things are fine.
For logged in users, minimize annoyance, and don't interrupt the message flow (don't insert anything between messages.)
I'd be fine with a skyscraper on the right. My preference would be a self serve system, as the multi-site solutions usually lead to non-targeted crap your audience is really not going to care about. Put another way, if you can get ads I want to see...I want to see them, but not be interrupted by them. Ads by contributors, for contributors, would be ideal. Let people buy/target topics (like search engines, webmaster business issues, etc.) Have a minimum click through rate where the ad will be auto canceled if not met within X,000 displays.