Debugging and troubleshooting webservices particularly after our website/application has gone live is always a nightmarish experience. This had been the case even in my previous organization. For a while then, I remember using this simple tool called WebService Studio by Sowmy (sowmys (at) microsoft.com). It is a pleasant and easy to use GUI which would manage invoking the WebMethods besides giving you comprehensive details on the various parameters that it takes.
I guess, it is open source too and hosted with GotDotNet workspaces over here. And I am sure this would greatly help developers worldwide to manage webservices easily.