Previously I've highlighted "Air Push", an intrusive technology that puts ads in your notification bar. And I've highlighted several apps that can scan for such intruders.
Let me introduce a new one, TrustGo Ad Detector.
It scans all the apps, then list the apps on potential ways it can cost you, such as make calls, send SMS, push ads to your phone, and so on.
Previously I was using Lookout Labs Ad Detector.
However, this one crashes on my Moto Droid Bionic, whereas TrustGo's work fine. So that one's gone, and I'm using this one.