VMM 2012 introduced comprehensive private cloud capabilities (maintained and expanded with R2). Through VMM, an organization can create private clouds, manage access to the private cloud and the underlying physical resources. App Contoller has taken on the role of the Self-Service portal (for Virtual Machine Manager) in a private cloud scenario (that can also expand your view in to any public e.g. Azure Cloud resources if needed). App Controller is a lightweight web based interface with a web front-end and a backend database component.

AppController is removed of the System Center suite since System Center 2016

Please note: The VMM Self-Service Portal is no longer supported in System Center 2012 SP1. Instead MS recommend that you use the App Controller (included in System Center) as the self-service portal solution.
Self-service users can also use the VMM console instead of the VMM Self-Service Portal to perform tasks, such as deploying virtual machines and services (but beware of users using admin portals), for details on the usage see http://bit.ly/17S4BWv

If you are using Service Manager then your organization can create Service Catalogues and offer those to self-service users (allowing you to surface pre-defined offerigs/services including approval and other processes). While Service Manager based offerings can be any service it can also include e.g. requests for private cloud infrastructure (like creating a new vm or a subscription to a cloud resource). Please note that Service Manager would typically not allow you to manage the actual cloud infrastructure itself. For an example of Service Manager integration see this video: http://bit.ly/1gT26fY
There is also a specific System Center Cloud Services Process Pack - updated to support System Center 2012 SP1. Its a service solution for automating the deployment of IaaS components. The CSPP once implemented offers a self-service experience using the Service Manager self-service portal to facilitate private cloud capacity requests, including the flexibility to request additional capacity as demands increase. See details/download here: http://bit.ly/102Du6w

If you are a Service Provider offering WS 2012 based cloud resources to tenants (running Enterprise workloads) then you could also consider the Azure Pack released in October 2013 (free to MS customers). The Windows Azure Pack is a collection of Windows Azure technologies that integrate with System Center and Windows Server to help provide a self-service portal for managing services such as websites, Virtual Machines, and Service Bus; a portal for administrators to manage resource clouds, scalable web hosting and more.
Essentially the Windows Azure Pack delivers the capabilities of Windows Azure into your datacenter, enabling you to offer a self-service, multi-tenant cloud with Windows Azure-consistent experiences and services. http://download.microsoft.com/download/0/1/C/01C728DF-B1DD-4A9E-AC5A-2C565AA37730/Windows_Azure_Pack_White_Paper.pdf

You can see from above that one of the challenges Microsoft faces is the integration of multiple tool and interfaces to provide a consistent, simplified admin and user experience.

In the next year, Microsoft will release Azure Stack which is a Microsoft Azure in your datacenter. This solution will be sold in CPS format (from 4 servers at least)