Good start, easily extensible.

The DDWRT forums have a full listing of OIDs that can be checked. For example, to check uptime:

# ddwrt uptime check:

define command{
command_name check_linksys_uptime
command_line $USER1$/check_snmp -H $HOSTADDRESS$ -C public -o 1.3.6.1.2.1.25.1.$
}