Windows: Perfmon Port or SNMP (depending upon monitoring model)
UNIX: SSH, Telnet (if not using SSH), SNMP (monitor dependent)
Firewalls: SNMP typically for network device monitoriong
DB: The port that the instance you are attempting to monitor is configured to use. Database solutions typically have a default well known port but this can be changed by the person installing the software. If your databse solution is installed on Windows and you have the integrated metrics packages for your DB then you may be able to pull most of the interesting stats through perfmon.
Weblogic: JMX Port as configured in your environment, SNMP (as appropriate to monitor)
.Net: You are really looking at perfmon stats here