linux:

sudo arp-scan --ignoredups --interface wlan0 --localnet



-------------------------------

nmap

nmap -sP 192.168.15.0/24

--------------------------------

mac os x

arp -a

-------------------


Other resources

    guide with better MAC address (/usr/share/arp-scan/mac-vendor.txt) lookup
    http://makezine.com/projects/build-raspberry-pi-network-scanner/