If you want more than just the online status of the servers you can use MRTG to generate graphics and make them accessible from the internet in html format. You can get information on traffic, users online, services, pretty much everything if you have a good SNMP daemon on the servers.
I've been using it this semester at a Network Configuration and Management class and it's pretty cool.
http://oss.oetiker.ch/mrtg/
http://net-snmp.sourceforge.net/