The new configuration transformation feature in Visual Studio 2010.
Edit by : Transfom Config lets you use the new configuration transformation feature in Visual Studio 2010 without performing a publish on a web application project. Just give it a source, transform and output and youre away!

How it works?
This project takes advantage of the MSBuild tasks that are distributed with VS2010. It reuses the assemblies and gives you more power over how and when you transform those configs. you can free download Transform Config Alpha now.