Our company uses 'Whats Up' by Ipswitch. Currently monitoring over 2500 devices such as servers, routers, temperature sensors.
You can ping devices, monitor for SNMP events, logged events in Windows, AIX, Linux, WMI monitoring, services, tasks....
Can create audio, visual, and email alerts, as well as SMS.
They license on a per-device basis as opposed to a per-port basis like SolarWinds.
Only thing I don't care for on this software is you can only run Microsoft SQL for a database. Can't use any open source solutions. The default install uses MS-SQL desktop version, but the db size is limited. If you need to go bigger, you have to install a full install of SQL on the server, or connect to a remote SQL server on your network to host your database (as we are).
My .02 cents...