1. Taking an existing application, and transferring it as is into a cloud provider. This is "forklifting".
2. Taking an application, and wrapping it up in cloud based provisioning and backup. This is the business space that RightScale and Zmanda help with.
3. Developing applications that implictly assume they are running in a cloud environment. I see a lot of talk of this, but not all that many running yet. But very soon they are going to be everywhere.