Does anyone know if it's possible to get serial numbers for network devices, specifically Cisco ASAs and EqualLogic SANs?
It's going to vary by device, however I know that for an ASA the OID 126.96.36.199.188.8.131.52.184.108.40.206. Should have the device serial number in it, so for that at least you can pull it via SNMP... Unfortunately there isn't really a "standard" for exactly what OID woudl contain the serial number, even within one manufacturer. For example for a Cisco 2960 switch it's actually in 220.127.116.11.18.104.22.168.2.19.
So basically you would have to determine if/where any particular device stores that using the MIB's for that specific device.