There’s a compiled list of official and community modules here.
Icinga Exchange allows you to share your modules too (choose
modules as category on creation). Use the intelligent search to select
modules from the categories drop down here.
Try a custom search.
Watch Eric’s introduction from Icinga Camp Berlin:
Carsten and myself did a talk on OSMC 2017 including Icinga Web 2 modules:
There also is a (German) training available here.
It is also worthwhile to look into the official modules and their code to learn best practices with the MVC framework and how hooks, controllers, views, etc do work in general.