I've been using this program for a little while now, and it's quite handy for more than it's stated purpose.
WakeMeOnLan
http://www.nirsoft.net/utils/wake_on_lan.html will scan your network subnet, list all devices it finds responding to a ping, and catalogue them by MAC address, manufacturer etc. It stores all this info in a .ini file.
Having first run the program with EVERY network device switched on, you can then use it subsequently to wake up any devices that are now switched off (it sends a wake up "magic packet" to the device).
I find this handy as I've several machines that don't have keyboard, screen or mouse (ie FTP server) - I can remotely wake them and then use remote desktop to connect to them.
The program is also useful just for automatically making a catalogue of all the devices on your network - whereas ip addreses might change through DHCP, this allows you to keep track of them, even to find what the current ip address is for the DHCP'd NAS disk you've not switched on for a month.
And it's totally free too.
The site
http://www.nirsoft.net/ seems to have quite a few handy little programs. None of them "install" - you just unzip them into a folder and run them - so they're easy to get rid of too.
Ian