Thought I'd just add a slight addition to the arping command:
arping -c 1 HOST_or_IPADDRESS | grep Unicast | sed -e 's/[A-Za-z0-9. ]* \[//' -e 's/\][ 0-9a-z.]*//'
This will run `arping` and request only one reply and then use `grep` and `sed` to get rid of all the extra information. (If all you want is the MAC address) I find this very useful if you have a list of hosts and want to create a loop that will output HOST MAC.