Roman Decker wrote an article about how to move virtual machine between vCenters that are not part of the same SSO domain, using PowerCLI.
I felt like it needed some adjustments to be more dynamic and interactive, so many of the hard coded bits I decided to make the script ask for at runtime.
Continue reading Cross SSO and vCenter VMotion using PowerCLI
If you need to search your vSphere Datastores for orphaned VMDK files, Luc Dekens made a script that can help you.
Another possibility is to use rvTools.