You can try the example service we've created in the trial cloud:
If anything's unclear or if you want additional services implemented to test against, let me know.
Webservice username: pop
webservice password: corn
There are several web services you can try at http://www.webservicex.net
I've used the currency converter one before
Use the currency convertor, thats the only one ive seen from the app store. http://www.webservicex.net/CurrencyConvertor