HTTP Debugger
A collegue of mine introduced me to Charles. It's an HTTP proxy that intercepts your web requests. Using this, you can inspect the requests a web site makes as well as the responses it receives. Not only does it show you the content of the HTTP requests/responses, but also the time the request/response took as well as the size of the response. But that's not all....if you phone now...(I digress) it also has throttling capability built in. This allows you to emulate a modem or various other connection lines.
We found it very usefull to determine the usability of our website and using it was definately an eye opener.
Very Cool :D