The free Compliance Checker for vSphere checks your environment against the security guidelines from the vSphere 4.0 Hardening Guide.
It checks up to 5 ESX/ESXi host for free. Just enter your vCenter server name or the IP address of an individual ESX/ESXi host and it performs the assessment. If you have more than 5 ESX/ESXi hosts in your environment the compliance checker only performs the assessment on the first 5.
The Compliance Checker generates a nice HTML report that displays the compliance rule that was checked and whether the host passed or failed the check according to best practices.
Each rule references a code from the Hardening Guide so that you can look up the recommendations and remediation steps.
Nice free utility, very useful in checking small (<5 host) environments for security hardening best practices.
Download the Free Compliance Checker for vSphere here.