I had a district show me a free IP tracking tool from SolarWinds. This tool would be good for any district who uses spreadsheets to track used and available IP addresses. The tool scans a particular subnet and reports on which IP's are used or free, how long it has been since it was used (which I think it gets from DNS), and it can also query devices using SNMP.
At minimum, I'd say that most of us have a small block of static addresses used for servers, printers, switches and countless other devices. This might be an easier way of keeping track of that info. There are additional features in a paid version of the tool, such as scheduling IP scans to take place at certain times and also assigning groups.
This may be a good tool for many of you. Here's a three-minute video from their company that discusses this tool: