Microsoft provides official webpage to list KMS client setup keys for some popular software such as Windows 8, Windows Server 2012 R2, Windows 7, Windows Vista, Windows Server 2008 etc.
But, these keys are only for the case you have KMS host.
However, you can use these keys to install those software but not activate. for example, in our company the software manager hold all product keys, if we have not a chance to meet him to get real product key, we used to input KMS key to let the installation process continue, later we can find our software manager to get real product key to activate the software.
Here are part of official KMS client setup keys:
Windows 8.1 Professional
Windows 8.1 Professional N
Windows 8.1 Enterprise
Windows 8.1 Enterprise N
Windows Server 2012 R2 Server Standard
Windows Server 2012 R2 Datacenter
Windows Server 2012 R2 Essentials
Please find all KMS Client setup Keys from here.