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 Michi did a talk on OSMC 2017 including Icinga Web 2 modules:
There’s a training module available here: Module Training
In 2019, our partner NETWAYS starts with their Icinga Web Module Development workshop.
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.