Whatsup is a simple to use but powerful management tool with a lot of functionality for supervision of sites, services and equipment.

Big brother is a simple foreseeable, web based application for supervision. It demands installation on the clients to get full client information. Available in a freeware version not to be used for commercial purpose more than a month.

Net Gong is a small and simple tool to monitor availability on all your network connected equipment and services. Trigs different type of alarms on discrepancy from normal behavior.

SNMPc is probably one of the first graphic management application for SNMP that was developed. SNMP has matured and so has SNMPc. Today it is a full powered management tool that includes most of the things you desire to a good pricing.