Came across Eucalyptus – Elastic Computing Architecture for Linking Your Programs to Useful Systems, a cloud infrastructure software that allows you to build and manage IaaS (Infrasture as a Service) cloud for the enterprise.
Eucalytus itself exposes its functionality (i.e. cloud management and control) via a web based interfaces thus allowing the applications and users using the cloud to seemlessly manage with the cloud infrastructure based on varying business needs.
The product is open source and allow you to build Linux image based clouds on top of common virtualization options.
Also check out this presentation on IaaS by Eucalyptus. A very useful insight by the founders of Eucalyptus on the current state of cloud computing with emphasis on private clouds, IaaS and how Eucalyptus addresses the needs.