Nmap is a great tool; utterly indispensable for network administrators. If you haven’t got it yet goto http://nmap.org or install via your favourite package manager.
Here’s one of my frequently used nmap commands – very simple, but gives you a quick list of IP addresses for all of the ProCurve switches on your network.
nmap -n -sP 10.0.0.0/24 | grep --before-context=1 "ProCurve Networking by HP" | grep "Host" | cut -f2 -d' '
Just change the subnet range to match your network. Note: this relies on doing vendor OUI lookups on device MAC addresses, which means that the scanning node needs to be on the same Layer 2 network segment for this to work.