Ask HN: Automation to monitor and control AWS usage?

My lab is moving towards using AWS for some of its computational needs. It's clear that really expensive mistakes are possible. (E.g., http://developer.amazonwebservices.com/connect/message.jspa?messageID=160180). I'm looking for automation which will warn you when AWS usage exceeds a certain burn-rate or absolute price. Ideally, it would shut the usage down automatically in some circumstances.