Fiddler by Eric Lawrence
Fiddler is a HTTP Debugging Proxy which logs all HTTP traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP Traffic, set breakpoints, and "fiddle" with incoming or outgoing data. Fiddler is designed to be much simpler than using NetMon or Achilles, and includes a simple but powerful JScript.NET event-based scripting subsystem.
Fiddler also allows you to record and play back the HTTP traffic as well as to export these recordings as Visual Studio Team System web tests. Currently, Fiddler has better support for AJAX web test recording then VSTS Test Edition. Check out this blog post by Eric Lee for more information.
Fiddler is made by Eric Lawrence of Microsoft and is available as a free download at http://www.fiddlertool.com.
