Telerik Fiddler

http://www.telerik.com/fiddler

Fiddler is an HTTP debugging proxy server application. Fiddler captures HTTP and HTTPS traffic and logs it for the user to review. Fiddler can also be used to modify HTTP traffic for troubleshooting purposes as it is being sent or received. By default, traffic from Microsoft's WinINET HTTP(S) stack is automatically directed to the proxy at runtime, but any browser or Web application can be configured to route its traffic through Fiddler.