http://www.badllama.com/content/monitor-varnish-zabbix
Handy little script to monitor varnish stats from zabbix. Awesome.
http://www.zabbix.com/forum/showthread.php?t=25265
A zabbix monitoring script for varnish ported from cacti.
http://cacti.net/
A web based tool to produce graphs based on data stored in RRDTool, usually used as a front end for data collected through systems like nagios.
https://www.linuxquestions.org/questions/linux-enterprise-47/nagios-vs-zabbix-216790/
A great discussion on the comparison between nagios and zabbix and other monitoring platforms. Very useful insights although a few years old.
http://tribily.com/
Hosted zabbiz service, starts at €5 per server per month. Not sure about data retention.
