Third party modules and plugins
Moodle has a database of modules and plugins (http://moodle.org/mod/data/view.php?id=6009) that you can make use of to enhance the functionality of your moodle website, please note that most of these modules and plugins are user contributed codes and they may not be completely verified by moodle, you should go through the user comments of the particular module to ensure there are :-
- Already a good number of users using this module
- The module developer is responsive and fixing bugs as user reports them, and the module is kept updated with latest moodle releases
- There is a good documentation for this module
This is important as you won't want to later discover the module is no longer active after you have extensively using it on your website and you are forced to remove it when there is a need to update the module in newer versions of moodle
Installing modules and plugins
Unlike some other popular CMS that follow a modular approach to third party plugins, moodle does not currently have a standard approach to install third party plugins, each plugins has their unique installation steps and generally introduces new files in the core moodle folders, you should be careful when selecting modules and try limit to a handful of third party modules, this can save you lots of time and effort when there is an upgrade exercise.