Time Synchronization
I'm very surprise that almost all of the clients I have worked at do not implement time synchronization of their servers and network equipment. This makes analyzing logs in an incident response and even for troubleshooting a headache. Many times what I recommend is using the Cisco router at each site as the time server for the site and have those sync with a central router. In virtual environments this becomes even more important since in heavy load the time in virtual machines will shift this why many times the DC with the PDC Master role is not virtualized or the virtualization tools on the VM's is set to force time synchronization.