source providers (RPs) focus on providing substantial communities with on-demand access to computing and storage. TeraGrid, Open Science Grid, campus grids, and the likes of Amazon EC2 and S3 fit in this space.
Service providers (SPs) use either dedicated resources or RP-provided resources to provide services to communities. Certificate authorities, Globus Reliable File Transfer service, and Amazon Simple Queue service are examples of hosted services.
Content providers (CPs) deliver application-specific content (data, software, etc.) to communities, using either dedicated or RP-/SP-provided resources and services. A TeraGrid "science gateway" is an example of a content provider that builds on resources and services provided by a third party.