OS X menubar/dashboard/dock utility for monitoring a server? Is there any desktop utility for OS X that would periodically monitor a (non-osx) server and display a status icon?  Something as simple as attempting to visit a URL every 5 minutes and turning red if it does not respond would be enough, although anything more detailed is interesting too.
GeekTool (free)

GeekTool will let you set up a simple icon or show more detailed information, embedded in or floating over your desktop, based on whatever programming you want. 

If you can write a script to check the server and return either a binary status or more detailed information, GeekTool is the way to display it.