Charles is an HTTP proxy/monitor that can assist with viewing traffic to assist with debugging applications. It has some cool key features, like viewing SSL requests/responses in plaintext, bandwidth throttling to simulate slower Internet connections, AJAX debugging, AMF to view Flash Remoting / Flex Remoting messages in a tree view, request repeating, replay tools, breakpoints, W3C validation tools, and more.
A senior developer showed me this the other day and we used it to conduct a simple load test. It's a pretty cool tool and much better than the standard Chrome/Firefox networking tools.
Link to Charles: https://www.charlesproxy.com/