Here are some very useful calculator links that we show many of our customers on the benefits of virtualization.
http://www.vmware.com/go/calculator = VMware TCO/ROI Calculator. Show the potential cost saving from VMware virtualization solutions and identifies the tangible CapEX and OpEX savings.
http://www.vmware.com/go/costperapp = When comparing Hypervisor products, it is best to compare "cost per application" (or VM) when using that hypervisor. Here is a calculator which shows how VMware can provide the lowest overall cost per app over other Hypervisors.
http://www.microsoft.com/Windowsserver2008/en/us/hyperv-calculators.aspx = Windows Licensing Calculator for Virtual Environments (when using Calculator #1, under “Virtualization Technology”, for VMware modify the configuration and choose 3rd-Party virtualization running on “bare metal”). This calculator will help you identifiy the Windows licensing cost savings when used in a virtual environment (when using any Hypervisor product like Hyper-V, vSphere, etc). More and more companies are using the unlimited Virtual Machines option that comes with the Windows Datacenter per CPU license which offers substantial cost savings on Windows licensing when virtualizing!