Are there any simple web based http monitoring open source tools I can run to remotely monitor web servers and such? I know about Nagios but I want a light install and unsure what exactly I should install (plugins etc.?)
Here is a Perl script for simple monitoring: http://perl.about.com/od/perltutorials/qt/servicemonitor.htm
But if you only need http monitoring (as opposed to monitoring server data like CPU usage or disk i/o) you can avoid any installation by using a hosted service like Pingdom.
Actually, it is even better to monitor externally in this case, since internal monitoring does not account for data center network issues (such as the 1and1 downtime last week).