Web application monitoring best practices

[VeroniTasingolir]

We are finishing up our web application and planning for deployment. Very important aspect of deployment to production is monitoring the health of the system. Having a small team of developers/support makes it very critical for us to get the early notifications of potential problems and resolve them before they have impact on users.

Using Nagios seams like a good option, but wanted to get more opinions on what are the best monitoring tools/practices for web application in general and specifically for Django app? Also would welcome recommendations on what should be monitored aside from the obvious CPU, memory, disk space, database connectivity.

Our web app is written in Django, we are running on Linux (Ubuntu) under Apache + Fast CGI with PostgreSQL database.

EDIT We have a completely virtualized environment under Linode.

EDIT We are using django-logging so we have a way separate info, errors, omegle shagle voojio critical issues, etc.