TulaFala looks to be pretting interesting. It is part of the Samoa Project from Microsoft Research in Cambridge. See http://securing.ws/. The description of the problem and the project sounds impressive, and useful:

An XML web service is, to a first approximation, a wide-area RPC service in which requests and responses are encoded in XML as SOAP envelopes, and transported over HTTP. Applications exist on the internet (for programmatic access to search engines and retail), on intranets (for enterprise systems integration), and are emerging between intranets (for the e-science Grid and for e-business). Specifications (such as WS-Security, now at OASIS) and early toolkits (such as Microsoft's WSE product) exist for securing web services by applying cryptographic transforms to SOAP envelopes.

The underlying principles, and indeed the difficulties, of using cryptography to secure RPC protocols have been known for many years, and there has been a sustained and successful effort to devise formal methods for specifying and verifying the security goals of such protocols. One line of work, embodied in the spi calculus of Abadi and Gordon and the applied pi calculus of Abadi and Fournet, has been to represent protocols as symbolic processes, and to apply techniques from the theory of the pi calculus, including equational reasoning, type-checking, and resolution theorem-proving, to attempt to verify security properties such as confidentiality and authenticity, or to uncover bugs.

The goal of the Samoa Project is to exploit recent theoretical advances in the analysis of security protocols in the practical setting of XML web services. Some early outcomes of this research include an implementation of declarative security attributes for web services and the design of a logic-based approach to checking SOAP-based protocols.

I haven't tried the tool yet, but if you do, please send some feedback to the people noted on that web page, or post some feedback to my blog and I'll route it to them.