I was having a problem with finding all of the mac addresses in my environment and waking them up with free tools.... and I didn't want to pay for something that I could write myself so... I wrote this script for powershell to check all of the leases from a DHCP server and wake them up or compile them into a list and then use that to wake them up at a later time. Technically you could just use the script to remotely get a list of all of the leases on a DHCP server.
I use this script so that I can wake and reboot the machines in my environment to install MSI's and other things since I don't allow my users to reboot or shutdown their systems.
Let me know if you guys find this useful or would like to see something else added to it.
http://gallery.technet.microsoft.com/Wake-on-Lan-for-DHCP-tool-3c2d8adf