The TcpTrace by Simon Fell, is one of those tools I can’t live without. It’s a proxy for TCP connections that shows actual content of messages exchanged between hosts. It always come handy when you need to see an actual Web Service call content or just check those HTTP headers 🙂
If youre looking for an axample to how to build similar tool look into Apache Soap source files: TcpTunnel.java and Relay.java
Windump (http://www.winpcap.org/windump/install/default.htm) is the best tool for such task :), I’m using it for years :).
TcpTrace is simpler in installation 😉