What kinds of printers do you have? If you have something like an HP JetDirect, you can press or hold down the reset button (check the manual first, though) to print a status page with the IP address.
I use SoftPerfect Network Scanner very often to find IP addresses on my network. It can be configured to scan for open web ports, which a printer would be using for its management interface. It will also display the mac address of everything on the network, with manufacture details, so you can sort it out to show what devices are of X brand, and then pick through them to find your lost devices.
Once you've found the info you need, start making labels!
If you've got quite a few printers, it might make sense to set up a print management server. I use the one built into Windows Server and am pretty happy with it. That way you can install and troubleshoot from one location and it keeps track of your printer info for you and provides drivers for all your clients.