I remember using a command line tool to flash a NIC's link light to identify it. I can't remember for the life of me what it was.
Is ethtool what you're looking for
ethtool --identify eth0
Ethtool also works with vmware ESXi with -p parameter:
ethtool -p vmnic0 15
vmnic0 will blink for 15 seconds
Here is a video that shows how it works (at 2:50 shows blink):