HP has a paper (PDF) reviewing various orchestration technologies, tools and standards.
Web services technologies are beginning to emerge as a defacto standard for integrating disparate applications and systems using open, XML-based standards. In addition to building web services interfaces to existing applications, there must also be a standard approach to connecting these web services together to form more meaningful business processes. In 2002, a number of new standards were introduced to address this problem, including BPEL4WS and WSCI. The purpose of this paper is to provide a review of these emerging standards, to help the reader better understand how web services orchestration can be accomplished today.