Webservius is a wrapper that provides for your web service APIs and data sources. Webservius handles billing, tools for your customers to use to monitor their use of your services, logging and use statistics, etc. They charge you 10% of what is billed through their service.
When I have a chance I will try the free version of this service (limited number of API calls per day and access to end users must be free) and write up the experience.
I noticed WebServius on Amazon's blog but Webservius is an independent company that uses the Amazon AWS platform.