Handy little script to monitor varnish stats from zabbix. Awesome.
A zabbix monitoring script for varnish ported from cacti.
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.
A great discussion on the comparison between nagios and zabbix and other monitoring platforms. Very useful insights although a few years old.
Hosted zabbiz service, starts at €5 per server per month. Not sure about data retention.