I started using Nagios many years ago. While the configuration is not complicated I always felt there was no reason to be administrating at the command line. Years ago I used a decent web interface - I believe it was called Fruity, but now with Nagios 3 I didn't see any updated support.
In comes NConf. I get nagios and NConf up and running but the I quickly run into Icinga which is a fork of Nagios. Always looking for the latest and greatest I try it out. The good news is it does everything Nagios does. The bad news is, it basically seems to do it the same way. After running Icinga from a basic administrative perspective I don't see the difference.
I'm running Ubuntu 10 on my server. To install I used the following article to setup Icinga on Ubuntu
http://www.fishfood.co.nz/2010/02/howto-to-tie-yucatan-knot.html
And then the following article to get NRPE (connection to remote monitoring) working.
http://www.crucialwebhost.com/blog/using-nrpe-to-monitor-remote-services/
These articles got me there but it wasn't as simple and straightforward as it should be.
Next I wanted to do remote monitoring of MySQL. I used the nagios check_mysql_health plugin. But even with it configured I needed to know values to set for warning and critical. I used this article as a starting point to assign these.
http://mikehathaway.com/sites/mikehathaway.com/files/mysql_demo.cfg
