Cloud Provider: An organization that makes a cloud computing environment available to others, such as an external or public cloud.
Reference: "Some workloads, such as application testing and training, are prime candidates for early deployment to a cloud provider due to their transient nature and high Total Cost of Ownership (TCO)." Source: John Janakiraman: Deploying Your Existing Applications to the Cloud

Cloud Enabler: A general term that refers to organizations (typically vendors) who are not cloud providers per se, but make available technology, such as cloudware, that enables cloud computing.

Cloud-Oriented Architecture (COA): An architecture for IT infrastructure and software applications that is optimized for use in cloud computing environments. The term is not yet in wide use, and as is the case for the term "cloud computing" itself, there is no common or generally accepted definition or specific description of a cloud-oriented architecture.
Reference: James Urquhart: The Principles of Cloud Oriented Architecture

Cloud Service Architecture (CSA): A term coined by Jeff Barr, chief evangelist at Amazon Web Services. The term describes an architecture in which applications and application components act as services on the cloud, which serve other applications within the same cloud environment.
Reference: Jeff Barr: The Emerging Cloud Service Architecture

Virtual Private Cloud (VPC): A term coined by Reuven Cohen, CEO and founder of Enomaly. The term describes a concept that is similar to, and derived from, the familiar concept of a Virtual Private Network (VPN), but applied to cloud computing. It is the notion of turning a public cloud into a virtual private cloud, particularly in terms of security and the ability to create a VPC across components that are both within the cloud and external to it.
Reference: "A VPC is a method for partitioning a public computing utility such as EC2 into quarantined virtual infrastructure. A VPC may encapsulate multiple local and remote resources to appear as a single homogeneous computing environment bridging the ability to securely utilize remote resources as part of an seamless global compute infrastructure." Source: Reuven Cohen: Life in the Cloud: Virtual Private Cloud

Cloud Portability: The ability to move applications (and often their associated data) across cloud computing environments from different cloud providers, as well as across private or internal cloud and public or external clouds.

Cloudsourcing - As defined by Dion Hinchcliffe: "Leveraging services in the network cloud to provide external computing capabilities, often to replace more expensive local IT capabilities.Cloudsourcing can theoretically provide significant economic benefits along with some attendant trade-offs. These trade-offs can include security and performance. The term "cloud" represents a set of external services on a 3rd party network, usually the Internet. The services can represent raw computing, storage, messaging, or more structured capabilities such as vertical and horizontal business applications, even community. These services are delivered over the network, but generally behave as if they are local." Read an overview of cloudsourcing by Dion Hinchcliffe.