I've been playing around with cool monitoring stuff today inbetween doing very boring CMS building in ASP (very unpleasent legacy code - pages and pages of global variables, redundant code and bugs).
Two things I have got working today - one on my R&D box (mandrake annoyingly never asked if I wanted the header and other files for everything so I have to install everything from scratch) and one on my live server.
On the live server I installed mytop - a toplike process monitor for mysql - its very cool, same interface as top and pretty clear.
On the R&D server I installed cricket and rrd. They have been slowly generating cummulitive charts. Pretty cool. If I had more time I would definately be up for adding network monitoring - at the moment its just monitoring page request times.
Both apps are written in perl natch