This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
I'm not sure that you need any web services specific notation on the use case diagram level. Text-based/goal-oriented use cases tend to be more useful anyway (see: Use Cases) and no special notation is required. Example: Web service use case: Travel reservation