The term "nagios-frontend" has sorta been mushed together into two separate things. They are:
1. as new website 'frontend' with a different look/new features
-Some popular ones are Centreon (prettifies everything), and nagios-php (a website frontend that uses PHP+MySQL instead of CGI)
- A GUI based configuration/setup 'frontend' for nagios.
-Some popular ones are Nagmin and fruity
Personally, i just use the nagios web frontend (and PnP for graphing)...but the default web frontend is ugly. So i use a little package of html & css files called Nuvola. Just copy the files over your nagios webroot and voila, pretty icons and colours.
As for configuration management, i generate mine with scripts and do all my editing via vim+console or regex. But if you're unfamiliar with nagios (and don't care if you ever aren't/need a quick inital setup), grab a config frontend. I've heard of Nagmin more often than not for that, but check out fruity too.