I'm in dire need of a program with... rather specific critera, and I don't expect it to be free:
Packets sent cannot be larger than 10-20kb to maintain network integrity
Command Line and GU interfaces
No Client side application in order to function
Compatible with Cisco switches
Modular incase of increased need of functions
Program cannot exceed more than 100mb
Ping at least 500 machines/switches per domain (1 primary domain, 8 child domains) and give average ping time
Give information about Windows Updates (If need to be installed, if need to be restarted due to installed updates)
Inform if anti-virus is up to date if one is installed
Pull full System Event Log
You can look at network hardware that should do this.. off the top of my head, I think SourceFire (google search it) should have something that will do exactly what you want, but it's in the thousands of dollars..
TopLayer.com may have something that would interest you also.
Ethereal might have some features you're looking for, which is a free download.
With those 3, you should be able to figure out what you need a do a google search to find good monitoring applications.
My company uses SolarWinds, an older version, which kind of sucks, but the newer versions look good.