Found a nice article on MSDN describing the various types of services - a taxonomy for services.
Jotting down the concepts explained in the article.
Entity Services - Expose/Surface business entities in the system.e.g. employee, customer, sales order,etc. They contain CRUD operations and additional domain specific operations - e.g. FindOrderByPrice Entity Services abstract the underlying datasources and persistence mechanisms.
Capability Services - Implement a specific business capability - for e.g. Pricing Service, Credit Card Processing Service, etc. They may use Entity Services for persistence.
Thus Entity Services are "data-centric" and Capability Services are "action-centric".
Process Services - Acts as a facade for a BPM process. Process services would maintain state due to the very nature of a workflow having to maintain state over a long running process. Process Services are typically implemented using BPM tools such as WWF, Biztalk, WPS, etc.
Infrastructure Services (Utility Services) - Common cross cutting functions such as Logging, Auditing, Security, Authorization, etc.