Argus is a system and network monitoring application. It will monitor nearly anything you ask it to monitor (TCP + UDP applications, IP connectivity, SNMP OIDS, etc). It presents a nice clean, easy to view web interface that will keep both the managers happy ("Red Bad. Green Good.") and the techs happy ("Ah! that's what the problem is"). It can send alerts numerous ways (such as via pager) and can automatically escalate if the techs fall asleep.