GOOD Network Monitoring tools???

i am currently trying to decide on a good network monitoring tool and am wondering what other people are using to monitor their networks. i need to monitor for various things, such as resource usage, services running, simple heartbeat, etc.

my network consists mainly of win2k machines, with some solaris 8 and red hat 7.2 machines and also cisco network components. since most all of my servers are compaq's, i have been using compaq's insight manager v7 for my network monitoring. doesn't seem to be a bad application, but does like to gobble up resources.

i have been looking at Alchemy-Labs "Alchemy-Eye 3.7" application (http://www.alchemy-lab.com/products/eye/), has anyone ever used this before? what did you think? it seems to have some nice functionality and additional plug-ins for added functionality.

thanks in advance for any suggestions you have.

http://www.ipswitch.com/Products/WhatsUp/index.html

What's Up Gold is a very nice product. It doesnt do resource usage monitoring, but it is very usefull for monitoring whether servers are up or down, the ability to tailor what ports it polls on for each server, allows you to get an idea when certain services have a problem as well.