HTTP Debugging Proxy that logs all HTTP traffic between your personal computer as well as the Internet
Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your pc and the Web. Fiddler enables you to scrutinize all HTTP(S) traffic, set breakpoints, and "fiddle" with incoming or outgoing data. Fiddler includes a strong eventbased scripting subsystem, and could be expanded using any.NET language.
Fiddler is freeware and can debug traffic from almost any program, including Mozilla Firefox, IE, Opera, and thousands more