Finally got around to installing my new shiny version of SoapScope, the little sniffer that could. I showed an early beta at TechEd 2003 in Dallas, but now it's released! It's wicked cheap, and when you're doing Web Services development in a workgroup situation, especially when the interface is in flux and the folks on the other side are in another time zone, it's slick.
It stores all the traffic in a built-in database and others can view and debug the service as it moves through time using a web interface served by it's internal (Apache) web server. It sniffs traffic via a packet capture OR as a proxy.
Two new features that I'm really digging are the WSDL Analyzer that checks for validity and compilance, and the Diff-er, that gives a sweet view of what's been changing from call to call, version to version.