Mac Address / IP Address

It seems to me if you can Ping an IP address there should be a way to get the Mac address of the Nic card associated with that IP address. I had thought by now there would be a utility out to assist in doing this. Someone had said you can get the mac address by using arp -a. , but only if you are on the same subnet. Any assistance here would be greatly appreciated. Thanks again. Have a good one!!