The Hardening Guide for vSphere v5.5 has been released and is now available here. If you are not familiar with the vSphere Hardening Guides, they can be used to help secure the majority of your VMware environment. It will not only help to ensure that your Virtual Machines are secure, but also the ESXi Hosts, Virtual Networks, vCenter Server and its components and Update Manager. Mike Foley has written a good blog about some of the changes to the tool here.
Finally, if you utilize vCenter Configuration Manager, you can import the vSphere Hardening Guides into vCM and automate the process of checking these different components for compliance. The best part is that if you do go out of compliance, you can be alerted to the fact and take appropriate action.