Maybe I overlooked it but I didn't see anyone posting the "UNITY" Game Engine here:
UNITY: Game Development Tool
The Positive: Deployment for Mac, Windows, Web-Deployment and Widget Deployment. The latest news is that you now create games for the Wii by using UNITY. Oh and almost forgot that you can use Unity to develop for the iphone as well (that is however still in beta as I believe).
The Negative: No Windows version as of yet. You will need a Mac at the moment in order to use the Unity Engine. Rumors has it though that they are working on a Windows port.