Download : http://www.charlesproxy.com/download/

Charles is an HTTP proxy / HTTP monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet. This includes requests, responses and the HTTP headers (which contain the cookies and caching information).

http://www.charlesproxy.com/assets/img/sm/23/image/mac_screen_321.png?k=f28bf8eff3