I've occasionally used network sniffers in the past, but with the rise of REST, XML, SOAP and .NET Remoting in the last year, sniffing has become an essential part of my development toolkit. I've evaluated a bunch of network sniffers, including the excellent open-source Ethereal, but the one I keep coming back to is Etherdetect:
This is a companion discussion topic for the original blog entry at: http://www.codinghorror.com/blog/2004/08/sniff-this.html