what are some popular OIDs that people are monitoring SNMP

Not sure if youve already checked the MIBs out, they can be downloaded via the firmware download section: https://support.fortinet.com/Download/FirmwareImages.aspx Check out the core mib inside the / FortiGate/ v5.00/ directory as well as the device specific mib in / FortiGate/ v5.00/ 5.2/ 5.2.0/ MIB/

My favourites, but you might have different preferences. CORE: Traps: .1.3.6.1.4.1.12356.100.1.3.0.101 Indicates that the CPU usage has exceeded the configured threshold. .1.3.6.1.4.1.12356.100.1.3.0.102 Indicates memory usage has exceeded the configured threshold. .1.3.6.1.4.1.12356.100.1.3.0.103 Log disk usage has exceeded the configured threshold. .1.3.6.1.4.1.12356.100.1.3.0.106 Power supply failure detected. .1.3.6.1.4.1.12356.100.1.3.0.108 A fan failure has been detected. FORTIGATE: Traps: .1.3.6.1.4.1.12356.101.2.0.402 Trap being sent when the HA cluster member changes its state .1.3.6.1.4.1.12356.101.2.0.601 A virus has been detected by the anti-virus engine .1.3.6.1.4.1.12356.101.2.0.503 An IPS signature has been triggered .1.3.6.1.4.1.12356.101.2.0.605 The anti-virus engine has entered conservation mode due to low memory conditions. Objects: .1.3.6.1.4.1.12356.101.4.1.7.0 Total hard disk capacity (MB). .1.3.6.1.4.1.12356.101.4.1.8.0 Number of active sessions on the device. .1.3.6.1.4.1.12356.101.4.1.4.0 Current memory utilization (percentage). .1.3.6.1.4.1.12356.101.4.1.3.0 Current CPU usage (percentage). .1.3.6.1.4.1.12356.101.13.2.1.1.5 Network bandwidth usage of the cluster member (kbps) .1.3.6.1.4.1.12356.101.3.1.2.0 The maximum number of virtual domains allowed on the device as allowed by hardware and/or licensing. .1.3.6.1.4.1.12356.101.3.1.1.0 The number of virtual domains in vdTable .1.3.6.1.4.1.12356.101.8.2.1.1.1 Number of virus transmissions detected in the virtual domain since start-up .1.3.6.1.4.1.12356.101.9.2.1.1.1 Number of intrusions detected since start-up in the VDOM. FORTIMANAGER Traps (most of the traps in the MIB are useful only with FortiAnalyzer): .1.3.6.1.4.1.12356.103.0.0.409 Indicates that the CPU usage excluding nice processes has exceeded the threshold. Objects: .1.3.6.1.4.1.12356.103.2.1.1.0 Current CPU usage (percentage) .1.3.6.1.4.1.12356.103.2.1.2.0 Current memory used (KB) .1.3.6.1.4.1.12356.103.2.1.3.0 Total physical and swap memory installed (KB) .1.3.6.1.4.1.12356.103.2.1.5.0 Total hard disk capacity (MB) .1.3.6.1.4.1.12356.103.2.1.4.0 Current hard disk usage (MB) There are also many interface-related objects you can monitor like in/outbound rate, packet errors, interface errors, etc. You just need to pick whichever you are interested in the best and configure them on your monitor server.