Free Tool: Virtualization Matrix
Here is a cool online tool to compare various aspects of VMware vSphere, Microsoft Hyper-V, and Citrix XenServer. This tool allows you to self-evaluate over 1000 individual features of VMware vSphere, Microsoft Hyper-V and Citrix XenServer. You can prioritize features and create a custom evaluation report for print/export.
You just pick the vendor, hypervisor, and editions you want to compare, and a comparison matrix is made for you. One thing to note that wasn't totally obvious to me though is that you need to expand the tree view on the left and select hypervisor editions in order for anything to show up. For example, expand VMware -> vSphere 5 -> Enterprise (by default, the editions are not chosen so you end up with an empty matrix).
Before you get started, I recommend watching this short tutorial video: