BACKGROUD: We currently are using TNT Software's ELM Enterprise Manger,
(http://www.tntsoftware.com/Products/EEM/), to notify admins of
certain warning and error events on a number of different Windows
2000/2003 servers.  However, we have not maintained our support and
have about 15 more server licenses to purchase to get us up to date. 
Due to the cost of this update, (I believe more than $5000).

REQUEST: We need to know what other options are available (including
pricing info for monitoring 25 servers).

The feature set we need are as follows:

 - email notification of certain events
 - custom event filtering (so that certain groups get only certain messages)
 - fail-over friendly (see notes below)

Optional but highly desirable features:
 - ping facility to notify admins if a machine is unavailable on the network
 - HTTP(S) website monitoring; verify page contents are the expected result
 - central console
 - stores events in a central database
 - some basic reporting mechanisms

In addition, we want to make sure that the system is fail-over
friendly.  That is, if a monitoring system is centrally executed on
one machine, we want to make sure to monitor that machine as well, in
case it fails.  So, if a product is licensed based on a central
repository, we will need two of those licenses so that they can
monitor each other.

We will need pricing info based on monitoring 25 Windows 2000/2003
servers and possibly 2 monitor licenses (if the product is designed
with a central monitoring service).

Please be sure to segregate options in the answer which clearly match,
might match and don't match but may be interesting.  Please ask any
questions if this is not clear!